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Upgrading & Repairing PCs Eighth Edition

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Hard Disk Drive Installation


This chapter thoroughly describes hard disk installation. In particular, the chapter examines the configuration, physical installation, and formatting of a hard disk drive. This chapter also covers the basic procedures necessary to install a hard disk drive into a PC system.

Hard Disk Installation Procedures

To install a hard drive in an IBM-compatible system, you must perform several procedures:

Drive configuration was discussed in Chapter 15, "Hard Disk Interfaces." For complete configuration information, consult the section that covers the type of drive that you are installing.

The following sections describe the other steps, which are simple to execute and, if done properly, result in the successful installation of a bootable hard disk. Special attention is given to issues of reliability and data integrity to ensure that the installation is long-lasting and trouble-free.

To begin the setup procedure, you need to know several details about the hard disk drive, controller or host adapter, and system ROM BIOS, as well as most of the other devices in the system. This information usually appears in the various OEM manuals that come with these devices. Make sure when you purchase these items that the vendor includes these manuals. (Many vendors do not include the manuals unless you ask for them.) For most equipment sold today, you will get enough documentation from the vendor or reseller of the equipment to enable you to proceed.

If you are like me, however, and want all the technical documentation on the device, you will want to contact the original manufacturer of the device and order the technical specification manual. For example, if you purchase an IBM-compatible system that comes with a Western Digital IDE hard disk, the seller probably will give you some limited information on the drive, but not nearly the amount that the actual Western Digital technical specification manual provides. To get this documentation, you have to call Western Digital and order it. The same goes for any of the other components in most clones that are assembled rather than manufactured. I find the OEM technical manuals to be essential in providing the highest level of technical support possible.

Here are a few of the major hard drive vendors' Web sites:

http://www.maxtor.com

http://www.micropolis.com

http://www.conner.com/toc.shtml

http://www.wdc.com/welcome.html

Controller Configuration

Configuring a disk controller involves setting the different system resources that the controller requires. Some controllers have these resources fixed, which means that they cannot be altered. Other controllers provide jumpers, switches, or even software that enable you to reconfigure or change the resources used. Controllers with adjustable resource settings often can be used in conjunction with other controllers in a system, but controllers with fixed resources usually cannot coexist with others.

All hard disk controllers and SCSI host adapters require one or more of the following system resources:

Not all adapters use every one of these resources, but some will use them all. In most cases, these resources must be configured so that they are unique and cannot be shared among several adapters. For example, if a disk controller is using I/O port addresses from 1F0-1F7h, no other device in the system can use those addresses.

When a conflict in resource use occurs, not all of the adapters involved may function. In the case of disk controllers, the controller will not function, and disk access will be impossible or corrupted. You need to identify which boards in the system have overlapping resources and then change the configuration of one or more of those boards to eliminate the conflict. Before installing a board, you should know which resources the board will require, and you should make sure that these resources are not being used by other boards.

In most systems, this is a manual procedure that requires you to know exactly what every adapter in the system is using. If your system supports Plug and Play (PnP), this will be much easier. On older MCA and EISA systems, the procedure is also under software control. PnP ISA, PCI, MCA, and EISA systems can automatically determine whether two adapters use the same resource and then change the configuration to eliminate the conflict.

For most systems, you need the documentation for every adapter in the system to ensure that no conflicts exist and to find out how to reconfigure a card to eliminate a conflict. Software included with your system, such as MSD (Microsoft Diagnostics, which comes with Windows 3.x and DOS 6.x) or the Device Manager in Windows 95, can help when documentation is not available or is limited. Aftermarket diagnostics and utility programs can also be helpful. Unless your system conforms to the PnP specification, software will normally not be able to identify direct conflicts, but if you install one board at a time, they can identify the addresses or resources that a given board is using.

Many system resources simply cannot be identified by software alone. Several companies, including AllMicro, Quarterdeck, Data Depot, and others manufacture cards that can be used to monitor interrupt and DMA channels. These boards are very helpful in identifying which of these resources are used in your system. These companies and others are listed in Appendix A.


NOTE: For more on software and hardware diagnostic tools, see Chapter 21, "Software and Hardware Diagnostic Tools." For additional information on interrupts and DMA channels, see also Chapter 5, "Bus Slots and I/O Cards."

ROM Addresses

Many disk controllers and SCSI host adapters require an on-board BIOS to function. An on-board BIOS can provide many functions, including:

If the motherboard BIOS supports a hard disk controller, an on-board BIOS is not needed--and in fact is undesirable because it uses memory in the Upper Memory Area (UMA). Fortunately, the on-board BIOS usually can be disabled if it is not required.

Only controllers that meet certain standards can run off the motherboard BIOS, including ST-506/412 controllers, ESDI controllers, and IDE bus adapters. These standards include the use of I/O port addresses 170-17Fh and interrupt 14. If you are installing a controller that uses other I/O port addresses or interrupt settings (such as when adding a second controller to a system), the motherboard BIOS will not be able to support it, and an on-board BIOS will be required. XT controllers universally need an on-board BIOS because the motherboard BIOS has no hard disk support whatsoever.

SCSI adapters normally do not emulate the WD1003-type disk interface and almost always require an on-board BIOS to provide disk driver functions. This on-board BIOS supports any of the adapter's settings; in most cases, multiple SCSI host adapters can use the BIOS of the first adapter, in which case the BIOSes on all but the first adapter can be disabled.

If an on-board BIOS is required and enabled, it will use specific memory address space in the UMA. The UMA is the top 384K in the first megabyte of system memory. The UMA is divided into three areas of two 64K segments each, with the first and last areas being used by the video-adapter circuits and the motherboard BIOS, respectively. Segments C000h and D000h are reserved for use by adapter ROMs such as those found on disk controllers or SCSI host adapters.


NOTE: You need to ensure that any adapters using space in these segments do not overlap with another adapter that uses this space. No two adapters can share this memory space. Most adapters have jumpers, switches, or even software that can adjust the configuration of the board and change the addresses that are used to prevent conflict.

Interrupt Request Channel (IRQ)

All disk controllers and SCSI host adapters require an interrupt line to gain the system's attention. These devices invoke a hardware interrupt to gain timely access to the system for data transfers and control. The original 8-bit ISA systems have only eight interrupt levels, with interrupts 2-7 available to any adapter. AT bus (16-bit ISA), EISA, and MCA systems have 16 interrupt levels, with interrupts 3-7, 9-12, and 14 and 15 available to any adapter cards. IRQs 10-12 and 14 and 15 are 16-bit interrupts available only to 16- or 32-bit adapters.

Tables 16.1 and 16.2 show the normally used and normally available interrupts in ISA, EISA, and MCA systems and in 8-bit ISA systems. The tables list the default use for each interrupt and indicate whether the interrupt is available in a bus slot.

Table 16.1  ISA, EISA, and MCA Default Interrupt Assignments

IRQ Function Bus Slot
0 System Timer No
1 Keyboard Controller No
2 Second IRQ Controller No
8 Real-Time Clock No
9 Network/Available (Redirected IRQ 2) Yes (8-bit)
10 Available Yes (16-bit)
  11 SCSI/Available Yes (16-bit)
  12 Motherboard Mouse Port Yes (16-bit)
  13 Math Coprocessor No
  14 Hard Disk Controller Yes (16-bit)
  15 Secondary IDE Yes (16-bit)
3 Serial Port 2 (COM2:) Yes (8-bit)
4 Serial Port 1 (COM1:) Yes (8-bit)
5 Sound/Parallel Port 2 (LPT2:) Yes (8-bit)
6 Floppy Disk Controller Yes (8-bit)
7 Parallel Port 1 (LPT1:) Yes (8-bit)

Table 16.2  XT-Bus (8-Bit ISA) Default Interrupt Assignments

IRQ Function Bus Slot
0 System Timer No
1 Keyboard Controller No
2 Network/Available Yes (8-bit)
3 Serial Port 2 (COM2:) Yes (8-bit)
4 Serial Port 1 (COM1:) Yes (8-bit)
5 Hard Disk Controller Yes (8-bit)
6 Floppy Disk Controller Yes (8-bit)
7 Parallel Port 1 (LPT1:) Yes (8-bit)

Notice that some of the interrupts are simply not available in slots; they are reserved for use only by the indicated system function. Any interrupt that is listed as being in use by an item that is not installed in your system would be available. For example, if your system does not have a motherboard mouse port, IRQ 12 would be available; if your system does not have a second serial port, IRQ 3 would be available.

You must discover which interrupts are currently in use and which are currently available in a system, and then configure any new cards to use only the available interrupts. In a standard configuration, the hard disk controller uses interrupt (IRQ) 14. Any secondary controllers would have to use other interrupts. The standard interrupt for a secondary controller is IRQ 15. If the system does not support EIDE (Enhanced IDE) in the motherboard BIOS, then any controllers that do not use IRQ 14 must have an on-board BIOS to function. The older motherboard BIOS supports disk controllers only at IRQ 14, whereas a BIOS with EIDE support will run IDE ports at both IRQ 14 and 15. Most newer systems have integral EIDE support and automatically include a secondary IDE port, which is at IRQ 15.

Standard IDE adapters come preconfigured for IRQ 14, which is fine if the adapter is the only disk adapter in the system. Many SCSI host adapters, such as the Adaptec 1540/1542C, come configured to one of the other available 16-bit interrupts, such as IRQ 11. Old XT (8-bit) hard disk controllers normally use IRQ 5.

DMA Channel

Direct Memory Access (DMA) is a technique for transferring blocks of data directly into system memory without the complete attention of the main processor. The motherboard has DMA control circuits that orchestrate and govern DMA transfers. In the original 8-bit XT bus, DMA was the highest-performance transfer method, and XT hard disk controllers universally used DMA channel 3 for high-speed transfers.

In AT-Bus (16-bit ISA) systems, most 16-bit disk controllers and SCSI host adapters do not use a DMA channel, partly because the performance of the AT Bus DMA circuitry turned out to be very poor. Therefore, most adapters use a technique called Programmed I/O (PIO), which simply sends bytes of data through the I/O ports. PIO transfers are faster than DMA transfers in most cases, especially if the motherboard BIOS and device support block-mode PIO, such as with the new IDE drives. If an adapter does not use DMA, you can assume that PIO is used as the data-transfer method and that no DMA channel is required.

Some adapters have found a way around the poor performance of the ISA bus by becoming what is known as a bus master. A bus master actually takes control of the bus and can override the DMA controller circuitry of the motherboard to perform fast DMA transfers. These transfers can exceed the performance of a PIO transfer (even block-mode PIO), so you will find that many of the highest-performing controllers have bus-master capabilities.

You have to select a DMA channel for bus-master adapters to use. In an 8-bit ISA bus, normally only DMA channel 1 is available; in a 16-bit ISA bus, however, DMA channels 0-1, 3, and 5-7 are available. DMA channels 5-7 are 16-bit channels that most high-performance bus-master adapters would want to use. XT disk controllers always use DMA channel 3, whereas most 16-bit AT or IDE controllers do not use DMA at all. This is not a concern in the newer PCI bus systems.

Tables 16.3 and 16.4 show the normally used and normally available DMA channels. The tables list the default use for each DMA channel and indicate whether the DMA channel is available in a bus slot.

Table 16.3  16-Bit ISA Default DMA Channel Assignments

DMA Function Transfer Bus Slot
0 Available 8-bit Yes(16-bit)
1 Sound/Available 8-bit Yes (8-bit)
2 Floppy Disk Controller 8-bit Yes (8-bit)
3 ECP Parallel/Available 8-bit Yes (8-bit)
  4 First DMA Controller N/A No
  5 Sound/Available 16-bit Yes(16-bit)
  6 SCSI/Available 16-bit Yes(16-bit)
  7 Available 16-bit Yes(16-bit)

Table 16.4  8-Bit ISA Default DMA Channel Assignments

DMA Function Transfer Bus Slot
0 Dynamic RAM Refresh N/A No
1 Sound/Available 8-bit Yes (8-bit)
2 Floppy Disk Controller 8-bit Yes (8-bit)
3 Hard Disk Controller 8-bit Yes (8-bit)

Notice that some of the DMA channels simply are not available in slots; they are reserved for use only by the indicated system function. Any DMA channel that is listed as being in use by an item that is not installed in your system would be available. For example, if your 8-bit ISA bus system does not have a hard disk controller, DMA channel 3 would be available.

PCI and EISA bus systems have additional DMA capabilities that support even faster transfers without the performance problems associated with non-bus-master cards. The PCI and EISA buses also provide even better support for bus-master devices that offer even higher performance.

To configure an adapter that requires a DMA channel, you first must find out which DMA channels currently are in use and which channels are available in your system. Unless you have an PCI or EISA system, software techniques for determining this are very limited. Most programs that claim to be capable of discovering which DMA channels are being used are only reporting what any standard configuration would be. In standard ISA systems, the only way to know for sure is to check the documentation for each adapter or to use a special hardware device that monitors DMA transfers.

After determining what DMA channels are free, you can set your adapter to any of those free channels. DMA conflicts usually result in improper operation or corrupted data transfers, so if you made a mistake, you usually will know quickly.

PCI and EISA systems automatically set up the boards so that no DMA conflicts exist. This method works fully only in EISA systems with all EISA 32-bit adapters installed. PCI buses usually have at least two or more ISA slots that you still need to worry about.

I/O Port Addresses

I/O port addresses are like mailboxes through which data and commands are sent to and from an adapter. These addresses are different from memory addresses. I/O ports must be used exclusively and cannot be shared among different adapters. Each adapter usually uses a group of sequential port addresses for communication with the bus.

The standard I/O port addresses used by disk controllers are 1F0-1F7h. These are the only addresses that the motherboard BIOS supports, so if you have a disk controller at any other port address, it must have an on-board BIOS. Obviously, if you are adding a secondary controller to a system, that controller must use different I/O addresses and also must have an on-board BIOS. Most controllers use 170-177h as secondary I/O addresses, which would be used if another disk controller were in the system; however, you can use any I/O addresses that are free.

I/O port conflicts are rare unless you are installing multiple disk controllers in a system. In that case, each controller needs different I/O port address settings so as not to conflict with the others. To determine what I/O ports are currently in use, you normally have to refer to the documentation that comes with each device in your system. Software normally cannot identify all used I/O port addresses unless you have a PCI or EISA system. When port conflicts exist, the devices in conflict do not function, or they function improperly.


Multi-Function I/O CardsMulti-function I/O cards are a combination floppy disk, hard disk, and serial and parallel port adapters all on one expansion card. Most newer motherboards have all these functions built right into the motherboard, but you may see a few of these multi-function boards in older PCI or VLB systems, and it is important to note that you will have to disable the hard disk controller on this board before installing a new controller.

Physical Installation

The procedure for physical installation of a hard disk is much the same as the procedure for installing a floppy drive. You must have the correct screws, brackets, and faceplates for the specific drive and system before you can install the drive.

Some AT or Baby-AT type computer cases require plastic rails that are secured to the sides of the drives so that they can slide into the proper place in the system (see Figure 16.1). Compaq uses a different type of rail, as does Hewlett-Packard, Packard Bell, and so on. When you purchase a drive, the vendor usually includes the "Standard-type" rails, so be sure to specify whether you need the special manufacturer type. IBM PC-type and XT-type systems do not need rails, but they may need a bracket to enable double-stacking of half-height drives. Several companies listed in Appendix B specialize in drive-mounting brackets, cables, and other hardware accessories. Also, many newer after market computer cases have eliminated the need for drive rails all together by making the expansion slot itself to the 3 1/2- or 5 1/4-inch drive specification, allowing you to bolt the new drive directly to the case itself.


NOTE: You should also note the length of the cable itself. In some cases, the drive cable is not long enough to reach the new drive location. You can try to reposition the original drive if you have the available expansion slots, or just get a longer cable.

Different faceplate, or bezel, options are available; make sure that you have the correct bezel for your application. Some systems, for example, do not need a bezel; if a bezel is on the drive, it must be removed. If you are installing a half-height drive in a full-height bay, you may need a blank half-height bezel to fill the hole, or you may want to order a half-height drive with a full-height bezel so that no hole is created. Several vendors listed in Appendix A sell a variety of drive mounting kits, hardware, rails, adapters, and cables.

FIG. 16.1  A full-height hard disk with AT mounting rails.


CAUTION: Make sure you use only the screws that come with your new drive. Many drives come with a special short-length screw that can have the same thread as other screws you might use in your system, but the shorter screws will not drive too far into the drive, which could cause problems.

System Configuration

When the drive is physically installed, you can begin configuring the system to the drive. You have to tell the system about the drive so that the system can boot from it when it powered on. How you set and store this information depends on the type of drive and system you have. Standard (IDE) setup procedures are used for most hard disks except SCSI drives. SCSI drives normally follow a custom setup procedure that varies depending on the host adapter that you are using. If you have SCSI drives, follow the instructions included with the host adapter to configure the drives.

Automatic Drive Typing

If the system is an AT type and you are using the mother-board BIOS to support the hard disks, you need to know some information about the BIOS, such as what drives are supported in the hard drive table. Many BIOS versions now have user-definable drive types that enable you to enter any set of parameters required to match your drive. For IDE drives, all new BIOS versions have automatic typing, which interrogates the drive and automatically enters the parameter information returned by the drive. This procedure eliminates errors or confusion in parameter selection.

If you are dealing with an older motherboard that does not support automatic typing, the information about the drive table appears in the technical manuals provided with the motherboard or the BIOS. Appendix A includes a list of drive types for many different BIOS versions. For systems that are not listed, you can find this information in the system's technical reference manual. Often, the BIOS setup program shows you all the available selections on-screen, enabling you to select the best choice interactively and eliminating the need to research this information.

Manual Drive Typing

After you collect the necessary information, the next step is to tell the system what kind of drive is attached so that the system can boot from the drive (eventually). This chapter discusses the installation of an example drive in an AT-type and ATX-type of system. With knowledge of drive interfacing, you can install just about any drive in any system.

First, you need to read the drive manual and locate the required information. The manual for this example contains the following drive-parameter information:

Cyl 188, Head 7 Cyl 601, Head 13
Cyl 217, Head 5 Cyl 798, Head 10
Cyl 218, Head 5 Cyl 835, Head 5
Cyl 219, Head 5

To install this drive in an AT-type case, I could simply use the original IDE drive; however, I would have to live with the relatively slow performance that this controller provides. A better choice is to upgrade the controller with an EIDE PIO mode 4 controller. This controller not only supports up to four IDE devices including CD-ROM, but will provide me with up to 16.6M/sec transfer rate.


NOTE: For more information on installation and configuration of drive controllers, see Chapter 15, "Hard Disk Interfaces."

The example controller uses PIO transfers and does not require a DMA channel for the hard disk controller portion. Because this controller also contains a floppy controller, some additional information specific to the floppy controller portion of the card is required:

You need some of this information to ensure that the card is uniquely configured compared with other cards in the system. The system cannot have other cards using the same IRQ, DMA, ROM, or I/O ports as this card. Keep this information for future reference, and cross-check for conflicts when you add other cards to the system. The step pulse rates and interleave information are all that you need to complete the setup.

After you find the information about the drive and controller, you need to match the drive's parameters to one of the drive-table entries in the motherboard ROM. ROM drive tables for IBM and many other compatible systems are listed in Appendix A, which also includes a detailed list of a large number of hard disk drives with parameter specifications. The information in Appendix A saved me several times when the original manuals were nowhere to be found. However, most drive tables are now embedded in the CMOS of the motherboard, and usually you have to choose User Defined (if you don't have an Auto-Configure option) option anyway, and fill in your new drive's parameters because most new drives are much larger than any of the available drive type choices.


TIP: The landing-cylinder designation is superfluous because all new drives automatically park and lock their heads at power-down, although it would be used if you ever ran a correctly written head-parking program.

This type of drive-table information does not apply to IBM ESDI or SCSI hard disk controllers, host adapters, and drives. Because ESDI and SCSI controllers and host adapters query the drive directly for the required parameters, no table-entry selection is necessary. The table for ST-506/412 drives, however, still appears in the ROM BIOS of most PS/2 systems, even if the model came standard with the ESDI or SCSI disk subsystem.

The manufacturers of most compatibles have enhanced the motherboard ROM BIOS tables in three ways:

As mentioned earlier, most of the newer compatible BIOS versions have both the user-definable type feature and automatic determination for IDE drives.

ROM Replacement

One way around the drive-table limits is to purchase and install a new ROM BIOS. A Phoenix ROM BIOS set, for example, costs about $50. These ROMs include a user-definable drive-type setting, which is the most elegant solution to this problem. A new set of ROMs probably will give you additional features, such as a built-in setup program, support for HD or ED 3 1/2-inch floppy drives, and Enhanced Keyboard support.

RLL/ESDI System Configuration

RLL and ESDI drives usually are not represented in the internal drive tables of older BIOS versions. Consequently, the controllers for these drives often have an on-board ROM BIOS that either contains an internal list of choices for the interface or enables you to dynamically configure (define) the controller to the specific geometry of the drive.

If you have a motherboard BIOS with a user-defined drive type (recommended), you can simply enter the correct parameters and the drive will be supported. (Remember to write down the parameters that you use; if you lose them, you can lose access to the drive if you don't re-enter the parameters properly.) When using a user-definable type, you can disable the controller BIOS.

IDE System Configuration

Intelligent IDE drives can use the geometry that represents their true physical parameters, or they can translate to other drive geometries that have the same number of sectors or fewer. Simply select a type, or enter a user-definable type that is less than or equal to the total capacity of the drive.

SCSI System Configuration

Almost all SCSI drives use DRIVE TYPE 0 or NONE, because the host adapter BIOS and the drive communicate to establish the drive geometry. The low-level formatting routines usually are accessed on the host adapter through a configuration, setup, and format program. All SCSI drives are low-level formatted at the factory.

Formatting and Software Installation

Proper setup and formatting are critical to a drive's performance and reliability. This section describes the procedures used to format a hard disk drive correctly. Use these procedures when you install a new drive in a system or immediately after you recover data from a hard disk that has been exhibiting problems.

Three major steps complete the formatting process for a hard disk drive subsystem:

Considerations Before Low-Level Formatting

In a low-level format (LLF), which is a "real" format, the tracks and sectors of the disk are outlined and written. During the LLF, data is written across the entire disk. An improper LLF results in lost data and in many read and write failures. You need to consider several things before initiating an LLF.

Data Backup

Low-level formatting is the primary standard repair procedure for hard disk drives that are having problems. Because data values are copied to the drive at every possible location during an LLF, necessary data-recovery operations must be performed before an LLF operation.


CAUTION: After an LLF has been performed, you cannot recover any information previously written to the drive.

Because an LLF overwrites all the data on a drive, it is a good way to erase an entire drive if you are trying to ensure that nobody will be able to get data from it. Government standards for this type of procedure actually require the data to be overwritten several times with different patterns, but for most intents and purposes, if the drive is overwritten one time, nobody will be able to read any data that was on it.

System Temperature

Sector header and trailer information is written or updated only during the LLF operation. During normal read and write activity, only the 512 bytes plus the CRC (Cyclic Redundancy Check) bytes in the trailer are written in a sector. Temperature-induced dimensional changes in the drive platters during read and write operations can become a problem.

When a 5 1/4-inch platter drive is low-level formatted five minutes after powerup at a relatively cold platter temperature of 70° F, the sector headers and trailers and the 512-byte dummy data values are written to each track on each platter at specific locations.

Suppose that you save a file on a drive that has been running for several hours at a platter temperature of 140° F. The data areas of only several sectors are updated. But with the drive platters as much as 70° warmer than when the drive was formatted, each aluminum drive platter will have expanded in size by 2.5 thousandths of an inch (taking into account the coefficient of linear thermal expansion of aluminum). Each track, therefore, would have moved outward a distance of approximately 1.25 thousandths of an inch. Most 5 1/4-inch hard disks have track densities between 500 and 1,000 TPI (tracks per inch), with distances of only 1 to 2 thousandths of an inch between adjacent tracks. As a result, the thermal expansion of a typical 5 1/4-inch hard disk platter could cause the tracks to migrate from one-half to more than one full track of distance below the heads. If the drive head-movement mechanism does not compensate for these thermally induced dimensional changes in the platters, severe mistracking results.

When mistracking occurs, the data areas in each sector that have been updated at the higher temperature fail to line up with the sector header and trailer information. If the sector header and trailer information cannot be read properly, DOS usually issues an error message like this one:

Sector not found reading drive C
Abort, Retry, Ignore, Fail?

The data is misaligned with the sector boundaries on those tracks. This thermal effect also can work in reverse: If the drive is formatted and written to while it is extremely hot, it may not read properly while cold because of dimensional changes in the platters. This problem occurs with drives that have the "Monday-morning blues," in which they spin but cannot read data properly when they are first powered on, especially after being off for an extended period (over a weekend, for example). If you leave the power to the system on for some time so that the drive can warm up, the system then may boot and run normally.

If this happens, the next step is to back up the drive completely and initiate a new LLF at the proper operating temperature (described next). This procedure enables the drive to work normally again until temperature-induced mistracking becomes great enough to cause the problem again.

Knowing that temperature fluctuations can cause mistracking, you should understand the reasons for the following basic rules of disk use:

If you have a cheap stepper motor drive that consistently exhibits temperature-related mistracking problems, you may want to consider running the drive constantly. Doing so would extend its trouble-free life span significantly because the temperature and dimensions of the platters would stay relatively constant.

These kinds of temperature-fluctuation problems are more of a problem with drives that have open-loop stepper motor actuators (which offer no thermal compensation) than with the closed-loop voice coil actuators (which follow temperature-induced track migration and compensate completely, resulting in no tracking errors even with large changes in platter dimensions).

Modern voice coil actuator drives do not exhibit these dimensional instabilities due to thermal expansion and contraction of the platters because they have a track-following servo mechanism. As the tracks move, the positioner automatically compensates. Many of these drives undergo a noticeable thermal compensation sequence every five minutes or so for the first 30 minutes after being powered on, and usually every 30 minutes after that. During these thermal-compensation routines, you hear the heads move back and forth as they measure and compensate for platter-dimension changes.

Drive Operating Position

Another consideration before formatting a drive is ensuring that the drive is formatted in the operating position it will have when it is installed in the system. Gravity can place on the head actuator different loads that can cause mistracking if the drive changes between a vertical and a horizontal position. This effect is minimized or even eliminated in most voice coil drives, but this procedure cannot hurt.

Additionally, drives that are not properly shock-mounted should be formatted only when they are installed in the system because the installation screws exert twisting forces on the drive's Head Disk Assembly (HDA), which can cause mistracking. If you format the drive with the mounting screws installed tightly, it may not read with the screws out, and vice versa. Be careful not to overtighten the mounting screws, because doing so can stress the HDA. This usually is not a problem if the drive's HDA is isolated from the frame by rubber bushings.

In summary, for a proper LLF, the drive should be

Because many different makes and models of controllers differ in the way that they write data to a drive, especially with respect to the encoding scheme, it is best to format the drive using the same make and model of controller as the controller that will be used in the host system. Some brands of controllers work exactly alike, however, so this is not an absolute requirement even if the interface is the same. This problem does not occur with IDE or SCSI drives, of course, because the controller is built into the drive. Usually, if the controller establishes the drive type by using its own on-board ROM rather than the system setup program, it will be incompatible with other controllers.

Low-Level Format

Of these procedures, the LLF is most important to ensure trouble-free operation of the drive. This format is the most critical of the operations and must be done correctly for the drive to work properly. The LLF includes several subprocedures:

On all new systems, these subprocedures are performed automatically by the system's LLF program and require no user intervention, and you need not continue in this section. On older systems, you must take the initiative, and should read on.

To perform the drive defect mapping, to select an interleave, and to complete a surface analysis of the drive, you need information about the drive, the controller, and possibly the system. This information usually is provided in separate manuals or documents for each item; therefore, be sure that you get the complete documentation for your drive and controller products when you purchase them. The specific information required depends on the type of system, controller, and LLF program that you are using.

Defect Mapping

Before formatting the disk, you need to know whether the drive has defects that have to be mapped out. Older drives came with a list of defects discovered by the manufacturer during the drive's final quality control testing. These defects were marked so that they are not used later to store programs or data.

Defect mapping was one of the most critical aspects of low-level formatting, now just a historical curiosity as low-level formatting is now done almost exclusively by the manufacturer. If you would like to understand the defect-mapping procedures, you first must understand what happens when a defect is mapped on a drive.

The manufacturer's defect list usually indicated defects by cylinder and track. When this information is entered, an LLF program marked these tracks with invalid checksum figures in the header of each of the sectors, ensuring that nothing can read or write to these locations. When DOS performed a high-level format of the disk, the DOS FORMAT program could not read these locations, and it marked the involved clusters in the File Allocation Table (FAT) so that they never will be used.

The list of defects that the manufacturer gives you probably is more extensive than what a program could determine from your system, because the manufacturer's test equipment is far more sensitive than a regular disk controller. The FORMAT program did not find the defects automatically; you probably had to enter them manually. The exceptions are new systems, in which the defect list is encoded in a special area of the drive that normal software cannot access. The LLF program (included in the motherboard BIOS program that comes with the systems) reads this special map, thereby eliminating the need to enter these locations manually.


TIP: If your motherboard BIOS does not have an LLF utility built in, you are probably better off not low-level formatting an IDE drive.

All new drives are low-level formatted by the manufacturer. If you bought a system with a drive already installed by the manufacturer or dealer, an LLF probably was done for you. Most manufacturers no longer recommend you LLF any IDE type drive.

Although an actual defect is technically different from a marked defect, these defects should correspond to one another if the drive is formatted properly. For example, I can enter the location of a good track into the LLF program as a defective track. The LLF program then corrupts the checksum values for the sectors on that track, rendering them unreadable and unwriteable. When the DOS FORMAT program encounters that track, it finds the track unreadable and marks the clusters occupying that track as being bad. After that, as the drive is used, DOS ensures that no data ever is written to that track. The drive stays in that condition until you redo the LLF of that track, indicate that the track is not to be marked defective, and redo the high-level format that no longer will find the track unreadable and therefore permit those clusters to be used. In general, unless an area is marked as defective in the LLF, it will not be found as defective by the high-level format, and DOS will subsequently use it for data storage.

Defect mapping becomes a problem when someone formats a hard disk and fails to enter the manufacturer's defect list, which contains actual defect locations, so that the LLF can establish these tracks or sectors as marked defects. Letting a defect go unmarked will cost you data when the area is used to store a file that you subsequently cannot retrieve.

Unfortunately, the LLF program does not automatically find and mark any areas on a disk that are defective. The manufacturer's defect list is produced by very sensitive test equipment that tests the drive at an analog level. Most manufacturers indicate areas as being defective even if they are just marginal. The problem is that a marginal area today may be totally unreadable in the future. You should avoid any area suspected as being defective by entering the location during the LLF so that the area is marked; then DOS is forced to avoid the area.

Currently Marked Defects Scan

Most LLF programs have the capability to perform a scan for previously marked defects on a drive. Some programs call this operation a defect scan; IBM calls it Read Verify in the IBM Advanced Diagnostics. This type of operation is nondestructive and reports by cylinder and head position all track locations marked bad. Do not mistake this for a true scan for defective tracks on a disk, which is a destructive operation normally called a surface analysis (discussed in the section "Surface Analysis" later in this chapter). If a drive was low-level formatted previously, you should scan the disk for previously marked defects before running a fresh LLF for several reasons:

If you run a surface analysis and encounter defects in addition to those on the manufacturer's list, you can do one of two things:

Manufacturer's Defect List

The manufacturer tests a new hard disk by using sophisticated analog test instruments that perform an extensive analysis of the surface of the platters. This kind of testing can indicate the functionality of an area of the disk with great accuracy, precisely measuring information such as the signal-to-noise ratio and recording accuracy.

Some manufacturers have more demanding standards than others about what they consider to be defects. Many people are bothered by the fact that when they purchase a new drive, it comes with a list of defective locations; some even demand that the seller install a defect-free drive. The seller can satisfy this request by substituting a drive made by a company with less-stringent quality control, but the drive will be of poorer quality. The manufacturer that produces drives with more listed defects usually has a higher-quality product because the number of listed defects depends on the level of quality control. What constitutes a defect depends on who is interpreting the test results.

To mark the manufacturer defects listed for the drive, consult the documentation for your LLF program. For most drives, the manufacturer's defect list shows the defects by cylinder and head; other lists locate the defect down to the bit on the track that is bad, starting with the index location.


CAUTION: Make sure that all manufacturer's defects have been entered before proceeding with the LLF.

Some systems automatically mark the manufacturer's defects, using a special defect file recorded on the drive by the manufacturer. For such a system, you need a special LLF program that knows how to find and read this file. Automatic defect-map entry is standard for IBM PS/2 systems and for most ESDI and all SCSI systems. Consult the drive or controller vendor for the proper LLF program and defect-handling procedures for your drive.


NOTE: Data recovery utilities such as ScanDisk (DOS/Windows) or Norton Utilities cannot mark the sectors or tracks at the physical format level. The bad cluster marks that they make are stored only in the FAT and are easily erased during the next high-level format operation. You should also use an LLF utility designed for your drive (contact the manufacturer), which will properly mark bad sectors and assign spares at the physical disk level.

Surface Analysis

A defect scan is a scan for marked defects; a surface analysis is a scan for actual defects. A surface analysis ignores tracks already marked defective by an LLF and tests the unmarked tracks. The surface-analysis program writes 512 bytes to each sector on the good tracks, reads the sectors back, and compares the data read to what was written. If the data does not verify, the program (like an LLF) marks the track bad by corrupting the checksum values for each sector on that track. A proper surface analysis is like an LLF program in that it should bypass the DOS and the BIOS so that it can turn off controller retry operations and also see when ECC (Error Correction Code) is invoked to correct soft errors.

Surface-analysis programs are destructive: They write over every sector except those that already are marked as bad. You should run a surface-analysis program immediately after running an LLF to determine whether defects have appeared in addition to the manu-facturer's defects entered during the LLF. A defect scan after the LLF and the surface analysis shows the cumulative tracks that were marked bad by both programs.

If you have lost the manufacturer's defect list, you can use the surface-analysis program to indicate which tracks are bad, but this program never can duplicate the accuracy or sensitivity of the original manufacturer testing.

Although it is recommended if you have been experiencing any problems with a drive, on new drives I normally do not run a surface analysis after low-level formatting for several reasons:

Why Low-Level Format?

Even though it generally is not necessary (or even recommended) to LLF IDE or SCSI drives, there are a few good reasons to consider an LLF. One reason is that an LLF will wipe out all the data on a drive, ensuring that other people will not be able to read or recover that data. This procedure is useful if you are selling a system and do not want your data to be readable by the purchaser. Another reason for wiping all the data from a drive is to remove corrupted or non-DOS operating-system partitions and even virus infections. The best reason is for defect management. As you may have noticed, most ATA-IDE drives appear to have no "bytes in bad sectors" under CHKDSK or any other software.

Any defects that were present on the drive after manufacturing were reallocated by the factory LLF. Essentially, any known bad sectors are replaced by spare sectors stored in different parts of the drive. If any new defects occur, such as from a minor head/platter contact or drive mishandling, a proper IDE-aware LLF program can map the new bad sectors to other spares, hiding them and restoring the drive to what appears to be defect-free status.

Because the IDE (ATA) specification is an extension of the IBM/WD ST-506/412 controller interface, the specification includes several new CCB commands that were not part of the original INT 13h/CCB support. Some of these new CCB commands are vendor-specific and are unique to each IDE drive manufacturer. Some manufacturers use these special CCB commands for tasks such as rewriting the sector headers to flag bad sectors, which in essence means LLF. When using these commands, the drive controller can rewrite the sector headers and data areas and then carefully step over any servo information (if the drive uses an embedded servo).

IDE drives can be low-level formatted, although some drives require special vendor- specific commands to activate certain LLF features and defect-management options. Seagate, Western Digital, Maxtor, IBM, and others make specific LLF and spare-sector defect-management software specific to their respective IDE drives. Conner drives are unique in that to actually LLF them, you need a special hardware device that attaches to a diagnostic port connector on the Conner IDE drive. A company called TCE (they are in the vendor list in Appendix A) sells such a device for $99. Coincidentally, this device is called The Conner. It includes software and the special adapter device that permits true low-level formatting (including rewriting all sectors and sector headers, as well as completely managing spare sector defects) at the factory level.

Other companies have developed LLF software that recognizes the particular IDE drive and uses the correct vendor-specific commands for the LLF and defect mapping. The best of these programs is Ontrack's Disk Manager. A general-purpose diagnostic program that also supports IDE-drive formatting is the MicroScope package by Micro 2000.

Intelligent IDE drives must be in nontranslating, or native, mode to LLF them. Zoned Recording drives can perform only a partial LLF, in which the defect map is updated and new defective sectors can be marked or spared, but the sector headers usually are rewritten only partially, and only for the purpose of defect mapping. In any case, you are writing to some of the sector headers in one form, and physical (sector-level) defect mapping and sector sparing can be performed. This procedure is, by any standard definition, an LLF.

On an embedded servo drive, all the servo data for a track is recorded at the same time by a specialized (usually laser-guided) servowriter. This servo information is used to update the head position continuously during drive function, so that the drive automatically compensates for thermal effects. As a result, all the individual servo bursts are in line on the track. Because the servo controls head position, there is no appreciable head-to-sector drift, as there could be on a nonservo drive.

This is why even though it is possible to LLF embedded servo drives, it rarely is necessary. The only purpose for performing an LLF on an embedded servo drive is to perform additional physical- (sector-) level defect mapping or sector sparing for the purpose of managing defects that occur after manufacture. Because no drift occurs, when a sector is found to contain a flaw, it should remain permanently marked bad; a physical flaw cannot be repaired by reformatting.

Most IDE drives have three to four spare sectors for each physical cylinder of the drive. These hundreds of spare sectors are more than enough to accommodate the original defects and any subsequent defects. If more sectors are required, the drive likely has serious physical problems that cannot be fixed by software.

Software for Low-Level Formatting

You often can choose among several types of LLF programs, but no single LLF program works on all drives or all systems. Because LLF programs must operate very closely with the controller, they often are specific to a controller or controller type. Therefore, ask the controller manufacturer for the formatting software it recommends.

If the controller manufacturer supplies an LLF program (usually in the controller's ROM), use that program, because it is the one most specifically designed for your system and controller. The manufacturer's program can take advantage of special defect-mapping features, for example. A different format program not only might fail to use a manufacturer-written defect map, but also might overwrite and destroy it.

For a general-purpose ST-506/412, ESDI, or IDE LLF program, I recommend the Disk Manager program by Ontrack. For the ST-506/412 interface only, I recommend the IBM Advanced Diagnostics or the HDtest program by Jim Bracking, a user-supported product found on many electronic bulletin boards, including CompuServe. (These companies are listed in the vendor list at the back of this book.) For SCSI systems and systems on which the other recommended programs do not work, you normally use will the format program supplied with the SCSI host adapter.

How Low-Level Format Software Works

There are several ways that a program can LLF a drive. The simplest way is to call the BIOS by using INT 13h functions such as the INT 13h, function 05h (Format Track) command. The BIOS then converts this command to what is called a CCB (Command Control Block) command: A block of bytes sent from the proper I/O ports directly to the disk controller. In this example, the BIOS would take INT 13h, 05h and convert it to a CCB 50h (Format Track) command, which would be sent through the Command Register Port (I/O address 1F7h for ST-506/412 or IDE). When the controller receives the CCB Format Track command, it may actually format the track or may simply fill the data areas of each sector on the track with a predetermined pattern.

The best way to LLF a drive is to bypass the ROM BIOS and send the CCB commands directly to the controller. Probably the greatest benefit in sending commands directly to the drive controller is being able to correctly flag defective sectors via the CCB Format Track command, including the capability to perform sector sparing. This is why IDE drives that are properly low-level formatted never show any bad sectors.

By using the CCB commands, you also gain the ability to read the Command Status and Error registers (which enable you to detect things such as ECC corrected data, which is masked by DOS INT 13h). You also can detect whether a sector was marked bad by the manufacturer or during a previous LLF and can maintain those marks in any subsequent Format Track commands, thereby preserving the defect list. I do not recommend unmarking a sector (returning it to "good" status), especially if the manufacturer previously marked it as bad.

When you use CCB commands, you can read and write sector(s) with automatic retries as well as ECC turned off. This capability is essential for any good surface analysis or LLF program, and this is why I recommend programs that use the CCB hardware interface rather than the DOS INT 13h interface.

Ontrack Disk Manager

For AT-type systems and other systems with controllers that do not have an autoconfigure routine, the Disk Manager program from Ontrack is excellent. It probably is the most sophisticated hard disk format tool available and has many capabilities that make it a desirable addition to your toolbox.

Disk Manager is a true register-level format program that goes around the BIOS and manipulates the disk controller directly. This direct controller access gives it powerful capabilities that simply are not possible in programs that work through the BIOS.

Some of these advanced features include the capability to set head- and cylinder-skew factors. Disk Manager also can detect intermittent (soft) errors much better than most other programs can, because it can turn off the automatic retries that most controllers perform. The program also can tell when ECC has been used to correct data, indicating that an error occurred, as well as directly manipulate the bytes that are used for ECC. Disk Manager has been written to handle most IDE drives and uses vendor-specific commands to unlock the capability to perform a true LLF on IDE drives.

All these capabilities make Disk Manager one of the most powerful and capable LLF programs available. Ontrack also offers an excellent package of hard disk diagnostic and data-recovery utilities called DOS Utils. Anybody who has to support, maintain, troubleshoot, repair, or upgrade PCs needs a powerful disk formatter such as Disk Manager.

HDtest

HDtest is an excellent BIOS-level format program that will function on virtually any drive that has an INT 13h ROM BIOS interface, which includes most drives. HDtest does not have some of the capabilities of true register-level format programs, but it can be used when the additional capabilities of a register-level program are not required. For example, you can use this program to do a quick wipe of all the data on a drive, no matter what the interface or controller type is. HDtest also is good for BIOS-level read and write testing, and has proved to be especially useful in verifying the functions of disk interface BIOS code.

HDtest, by Jim Bracking, is a user-supported software program. This program is distributed through electronic bulletin boards and public-domain software libraries. You also can obtain the program from the Public Software Library, listed in Appendix A. It costs $35, but you can try it for free.

HDtest has an easy-to-use interface and pull-down menu system. The program offers all functions that normally are associated with a standard LLF program, as well as some extras:

HDtest includes most of what you would want in a generic LLF program and hard disk diagnostics utility. Its real limitation is that it works only through the BIOS and cannot perform functions that a true register-level format program can. In some cases, the program cannot format a drive that a register-level program could format. Only register-level programs can perform defect mapping in most IDE and SCSI environments.

SCSI Low-Level Format Software

If you are using a SCSI drive, you must use the LLF program provided by the manufacturer of the SCSI host adapter. The design of these devices varies enough that a register-level program can work only if it is tailored to the individual controller. Fortunately, all SCSI host adapters include such format software, either in the host adapter's BIOS or in a separate disk-based program.

The interface to the SCSI drive is through the host adapter. SCSI is a standard, but there are no true standards for what a host adapter is supposed to look like. This means that any formatting or configuration software will be specific to a particular host adapter. For example, IBM supplies formatting and defect-management software that works with the IBM PS/2 SCSI host adapters directly on the PS/2 Reference disk. That software performs everything that needs to be done to a SCSI hard disk connected to an IBM host adapter. IBM has defined a standard interface to its adapter through an INT 13h and INT 4Bh BIOS interface in a ROM installed on the card. The IBM adapters also include a special ABIOS (Advanced BIOS) interface that runs in the processor's protected mode of operation (for use under protected-mode operating systems such as OS/2).

Other SCSI host adapters often include the complete setup, configuration, and formatting software in the host adapter's on-board ROM BIOS. Most of these adapters also include an INT 13h interface in the BIOS. The best example is the Adaptec 1540/1542C adapters, which include software in ROM that completely configures the card and all attached SCSI devices.


NOTE: Notice that SCSI format and configuration software is keyed to the host adapter and is not specific in any way to the particular SCSI hard disk drive that you are using.

IDE Low-Level Format Software

IDE drive manufacturers have defined extensions to the standard WD1002/1003 AT interface, which was further standardized for IDE drives as the ATA (AT Attachment) interface. The ATA specification provides for vendor-unique commands, which are manufacturer proprietary extensions to the standard. To prevent improper low-level formatting, many of these IDE drives have special codes that must be sent to the drive to unlock the format routines. These codes vary among manufacturers. If possible, you should obtain LLF and defect-management software from the drive manufacturer; this software usually is specific to that manufacturer's products.

The custom nature of the ATA interface drives is the source of some myths about IDE. Many people say, for example, that you cannot perform an LLF on an IDE drive, and that if you do, you will wreck the drive. This statement is untrue! What can happen is that in some drives, you may be able to set new head and sector skew factors that are not as optimal for the drive as the ones that the manufacturer set, and you also may be able to overwrite the defect-map information. This situation is not good, but you still can use the drive with no problems provided that you perform a proper surface analysis.

Most ATA IDE drives are protected from any alteration to the skew factors or defect map erasure because they are in a translated mode. Zoned Recording drives always are in translation mode and are fully protected. Most ATA drives have a custom command set that must be used in the format process; the standard format commands defined by the ATA specification usually do not work, especially with intelligent or Zoned Recording IDE drives. Without the proper manufacturer-specific format commands, you will not be able to perform the defect management by the manufacturer-specified method, in which bad sectors often can be spared.

Currently, the following manufacturers offer specific LLF and defect-management software for their own IDE drives:

These utilities are available for downloading on the various BBSes run by these companies. The numbers appear in Appendix A.

Conner Peripherals drives are unique in that they cannot be low-level formatted through the standard interface; they must be formatted by a device that attaches to a special diagnostics and setup port on the drive. You see this device as a 12-pin connector on Conner drives. A company called TCE sells an inexpensive device that attaches your PC to this port through a serial port in your system, and includes special software that can perform sophisticated test, formatting, and surface-analysis operations. The product is called The Conner. (TCE is listed in Appendix A.)

For other drives, I recommend Disk Manager by Ontrack, as well as the MicroScope program by Micro 2000. These programs can format most IDE drives because they know the manufacturer-specific IDE format commands and routines. They also can perform defect-mapping and surface-analysis procedures.

Nondestructive Formatters

General-purpose, BIOS-level, nondestructive formatters such as Calibrate and SpinRite are not recommended in most situations for which a real LLF is required. These programs have several limitations and problems that limit their effectiveness; in some cases, they can even cause problems with the way defects are handled on a drive. These programs attempt to perform a track-by-track LLF by using BIOS functions, while backing up and restoring the track data as they go. These programs do not actually perform a complete LLF, because they do not even try to LLF the first track (Cylinder 0, Head 0) due to problems with some controller types that store hidden information on the first track.

These programs also do not perform defect mapping in the way that standard LLF programs do, and they can even remove the carefully applied sector header defect marks during a proper LLF. This situation potentially allows data to be stored in sectors that originally were marked defective and may actually void the manufacturer's warranty on some drives. Another problem is that these programs work only on drives that are already formatted and can format only drives that are formattable through BIOS functions.

A true LLF program bypasses the system BIOS and send commands directly to the disk controller hardware. For this reason, many LLF programs are specific to the disk controller hardware for which they are designed. It is virtually impossible to have a single format program that will run on all different types of controllers. Many hard drives have been incorrectly diagnosed as being defective because the wrong format program was used and the program did not operate properly.

Drive Partitioning

Partitioning a hard disk is the act of defining areas of the disk for an operating system to use as a volume. To DOS, a volume is an area of a disk denoted as a drive letter; for example, drive C is volume C, drive D is volume D, and so on. Some people think that you have to partition a disk only if you are going to divide it into more than one volume. This is a misunderstanding; a disk must be partitioned even if it will be the single volume C.

When a disk is partitioned, a master partition boot sector is written at cylinder 0, head 0, sector 1--the first sector on the hard disk. This sector contains data that describes the partitions by their starting and ending cylinder, head, and sector locations. The partition table also indicates to the ROM BIOS which of the partitions is bootable and, therefore, where to look for an operating system to load. A single hard disk can have 1 to 24 partitions. This number includes all the hard drives installed in the system, which means that you can have as many as 24 separate hard disks with one partition each, a single hard disk with 24 partitions, or a combination of disks and partitions such that the total number of partitions is no more than 24. If you have more than 24 drives or partitions, DOS does not recognize them, although other operating systems may. What limits DOS is that a letter is used to name a volume, and the Roman alphabet ends with Z--the 24th volume, when you begin with C.

FDISK

The DOS FDISK program is the accepted standard for partitioning hard disks. Partitioning prepares the boot sector of the disk in such a way that the DOS FORMAT program can operate correctly; it also enables different operating systems to coexist on a single hard disk.

If a disk is set up with two or more partitions, FDISK shows only two total DOS partitions: the primary partition and the extended partition. The extended partition then is divided into logical DOS volumes, which are partitions themselves. FDISK gives a false impression of how the partitioning is done. FDISK reports that a disk divided as C, D, E, and F is set up as two partitions, with a primary partition having a volume designator of C and a single extended partition containing logical DOS volumes D, E, and F. But in the real structure of the disk, each logical DOS volume is a separate partition with an extended partition boot sector describing it. Each drive volume constitutes a separate partition on the disk, and the partitions point to one another in a daisy-chain arrangement.

The minimum size for a partition in any version of DOS is one cylinder; however, FDISK in DOS 4 and later versions allocates partitions in megabytes, meaning that the minimum-size partition is 1M. DOS 4.x and later versions permit individual partitions or volumes to be as large as 2G, whereas versions of DOS earlier than 4.0 have a maximum partition size of 32M.

The current DOS (version 7 underlying Windows 95 OSR2) supports partition sizes of up to 2T using FAT 32.

FDISK Undocumented Functions

FDISK is a very powerful program, and in DOS 5 and later versions, it gained some additional capabilities. Unfortunately, these capabilities were never documented in the DOS manual and remain undocumented even in DOS 7. The most important undocumented parameter in FDISK is the /MBR (Master Boot Record) parameter, which causes FDISK to rewrite the Master Boot Sector code area, leaving the partition tables intact.


CAUTION: Beware: It will overwrite the partition tables if the two signature bytes at the end of the sector (55AAh) are damaged. This situation is highly unlikely, however. In fact, if these signature bytes were damaged, you would know; the system would not boot and would act as though there were no partitions at all.

The /MBR parameter seems to be tailor-made for eliminating boot-sector virus programs that infect the Master Partition Boot Sector (Cylinder 0, Head 0, Sector 1) of a hard disk. To use this feature, you simply enter

FDISK /MBR

FDISK then rewrites the boot sector code, leaving the partition tables intact. This should not cause any problems on a normally functioning system, but just in case, I recommend backing up the partition table information to floppy disk before trying it. You can do this with the following command:

MIRROR /PARTN

This procedure uses the MIRROR command to store partition-table information in a file called PARTNSAV.FIL, which should be stored on a floppy disk for safekeeping. To restore the complete partition-table information, including all the master and extended partition boot sectors, you would use the UNFORMAT command as follows:

UNFORMAT /PARTN

This procedure causes the UNFORMAT command to ask for the floppy disk containing the PARTNSAV.FIL file and then to restore that file to the hard disk.

Note that if you are using Windows 95, the MIRROR and UNFORMAT programs have been eliminated, and you will have to purchase Norton Utilities instead.

FDISK also has three other undocumented parameters: /PRI:, /EXT:, and /LOG:. These parameters can be used to have FDISK create master and extended partitions, as well as logical DOS volumes in the extended partition, directly from the command line rather than through the FDISK menus. This feature was designed so that you can run FDISK in a batch file to partition drives automatically. Some system vendors probably use these parameters (if they know about them, that is!) when setting up systems on the production line. Other than that, these parameters have little use for a normal user, and in fact may be dangerous!

Other Partitioning Software

Since DOS 4, there has been little need for aftermarket disk partitioning utilities, except in special cases. If a system is having problems that cause you to consider using a partitioning utility, I recommend that you upgrade to a newer version of DOS instead. Using nonstandard partitioning programs to partition your disk jeopardizes the data in the partitions and makes recovery of data lost in these partitions extremely difficult.

The reason why disk partitioning utilities other than FDISK even existed is that the maximum partition size in older DOS versions was restricted: 16M for DOS 2.x and 32M for DOS 3.x. These limits are bothersome for people whose hard disks are much larger than 32M, because they must divide the hard disk into many partitions to use all of the disk. Versions of DOS before 3.3 cannot even create more than a single DOS-accessible partition on a hard disk. If you have a 120M hard disk and are using DOS 3.2 or an earlier version, you can access only 32M of that disk as a C partition.

To overcome this limitation, several software companies created enhanced partitioning programs which you can use rather than FDISK. These programs create multiple partitions and partitions larger than 32M on a disk that DOS can recognize. These partitioning programs include a high-level format program, because the FORMAT program in DOS 3.3 and earlier versions can format partitions only up to 32M.

Disk Manager by Ontrack is probably the best-known of the partitioning utilities. These programs include LLF capabilities, so you can use one of them as a single tool to set up a hard disk. The programs even include disk driver software that provides the capability to override the physical type selections in the system ROM BIOS, enabling a system to use all of a disk, even though the drive-type table in the system ROM BIOS does not have an entry that matches the hard disk.

Many drive vendors and integrators gave away these nonstandard partitioning and formatting programs, which makes some purchasers of such products feel that they must use those drivers to operate the drive. In most cases, however, better alternatives are available; nonstandard disk partitioning and formatting can cause more problems than it solves.

For example, Seagate shipped Ontrack Disk Manager with its drives larger than 32M. One purpose of the program is to perform low-level formatting of the drive, which Disk Manager does well, and I recommend it highly for this function. If possible, however, you should avoid the partitioning and high-level formatting functions and stick with FDISK and FORMAT.

When you use a program other than standard FDISK and FORMAT to partition and high-level (DOS) format a drive, the drive is set up in a nonstandard way, different from pure DOS. This difference can cause trouble with utilities--including disk cache programs, disk test and interleave check programs, and data recovery or retrieval programs--written to function with a standard DOS disk structure. In many situations that a standard format would avoid, a nonstandard disk format can cause data loss and also can make data recovery impossible.


CAUTION: You should use only standard DOS FDISK and FORMAT to partition or high-level format your hard disks. If you use aftermarket partitioning software to create a nonstandard disk system, some programs that bypass DOS for disk access will not understand the disk properly and may write in the wrong place. Windows is an example of a program that bypasses DOS when you turn on the Use 32-bit Disk Access option in the Control Panel.

It is especially dangerous to use these partitioning programs to override your ROM BIOS disk-table settings. Consider the following disaster scenario.

Suppose that you have a Seagate ST-4096 hard disk, which has 1,024 cylinders and nine heads, and requires that your controller never perform a data-write modification called write precompensation to cylinders of the disk. Some drives require this precom-pensation on the inner cylinders to compensate for the peak shifting that takes place because of the higher density of data on the (smaller) inner cylinders. The ST-4096 internally compensates for this effect and therefore needs no precompensation from the controller.

Now suppose that you install this drive in an IBM AT that does not have a ROM BIOS drive table that matches the drive. The best matching type you can select is type 18, which enables you to use only 977 cylinders and seven heads--56.77M of what should be a 76.5M hard disk. If your IBM AT is one of the older ones with a ROM BIOS dated 01/10/84, the situation is worse, because its drive-table ends with type 14. In that case, you would have to select type 12 as the best match, giving you access to 855 cylinders and seven heads, or only 49.68M of a 76.5M drive.

ROM BIOS drive tables are listed in Appendix A. Most IBM-compatibles have a more complete drive-type table and would have an exact table match for this drive, allowing you to use the full 76.5M with no problems. In most compatibles with a Phoenix ROM BIOS, for example, you would select type 35, which would support the drive entirely.

Now suppose that you are not content with using only 50M or 57M of this 76.5M drive. You invoke the SuperPartition aftermarket partitioning program that came with the drive and use it to LLF the drive. Then you use the aftermarket program to override the type 18 or type 12 settings in the drive table. The program instructs you to set up a very small C partition (of only 1M) and then partitions the remaining 75.5M of the disk as D. This partitioning overrides the DOS 3.3 32M partition limitation. (If you had an IBM-compatible system that did not require the drive-type override, you still would need to use the aftermarket partitioner to create partitions larger than the DOS 3.3 standard 32M.) Following that, you use the partitioner to high-level format the C and D partitions, because the DOS high-level format in DOS 3.3 works only on volumes of 32M or less.

Most aftermarket partitioners create a special driver file that they install in the CONFIG. SYS file through the DEVICE command. After the system boots from the C partition and loads the device driver, the 75.5M D partition is completely accessible.

Along comes an innocent user of the system who always boots from her own DOS floppy disk. After booting from the floppy, she tries to log into the D partition. No matter what version of DOS this user boots from on the floppy disk, the D partition seems to have vanished. An attempt to log into that partition results in an Invalid drive specification error message. No standard version of DOS can recognize that specially created D partition if the device driver is not loaded.

An attempt by this user to recover data on this drive with a utility program such as Norton or PC Tools results in failure, because these programs interpret the drive as having 977 cylinders and seven heads (type 18) or 855 cylinders and seven heads (type 12). In fact, when these programs attempt to correct what seems to be partition-table damage, data will be corrupted in the vanished D partition.

Thinking that there may be a physical problem with the disk, the innocent user boots and runs the Advanced Diagnostics software to test the hard disk. Because Advanced Diagnostics incorporates its own special boot code and does not use standard DOS, it does not examine partitioning but goes to the ROM BIOS drive-type table to determine the capacity of the hard disk. It sees the unit as having only 977 or 855 cylinders (indicated by the type 18 or 12 settings), as well as only seven heads. The user then runs the Advanced Diagnostics hard disk tests, which use the last cylinder of the disk as a test cylinder for diagnostic read and write tests. This cylinder subsequently is overwritten by the diagnostics tests, which the drive passes because there is no physical problem with the drive.

This innocent user has just wiped out the D-drive data that happened to be on cylinder 976 in the type-18 setup or on cylinder 854 in the type-12 setup. Had the drive been partitioned by FDISK, the last cylinder indicated by the ROM BIOS drive table would have been left out of any partitions, being reserved so that diagnostics tests could be performed on the drive without damaging data.

Beyond the kind of disaster scenario just described, other potential problems can be caused by nonstandard disk partitioning and formatting, such as the following:

  • Problems in using the 32-bit Disk Access feature provided by Windows, which bypasses the BIOS for faster disk access in 386 Enhanced Mode.

  • Data loss by using OS/2, UNIX, XENIX, Novell Advanced NetWare, or other non-DOS operating systems that do not recognize the disk or the nonstandard partitions.

  • Difficulty in upgrading a system from one DOS version to another.

  • Difficulty in installing a different operating system, such as OS/2, on the hard disk.

  • Data loss by using an LLF utility to run an interleave test; the test area for the interleave test is the diagnostics cylinder, which contains data on disks formatted with Disk Manager.

  • Data loss by accidentally deleting or overwriting the driver file and causing the D partition to disappear after the next boot.

  • Data-recovery difficulty or failure because nonstandard partitions do not follow the rules and guidelines set by Microsoft and IBM, and no documentation on their structure exists. The sizes and locations of the FATs and root directory are not standard, and the detailed reference charts in this book (which are valid for an FDISK-created partition) are inaccurate for nonstandard partitions.

I could continue, but I think you get the idea. If these utility programs are used only for low-level formatting, they do not cause problems; it is the drive-type override, partitioning, and high-level format operations that cause difficulty. If you consider data integrity to be important, and you want to be able to perform data recovery, follow these disk support and partitioning rules:

  • Every hard disk must be properly supported by system ROM BIOS, with no software overrides. If the system does not have a drive table that supports the full capacity of the drive, accept the table's limit, upgrade to a new ROM BIOS (preferably with a user-definable drive-type setting), or use a disk controller with an on-board ROM BIOS for drive support.

  • Use only FDISK to partition a hard disk. If you want partitions larger than 32M, use DOS 4 or a later version.

High-Level (Operating-System) Format

The final step in the software preparation of a hard disk is the DOS high-level format. The primary function of the high-level format is to create a FAT and a directory system on the disk so that DOS can manage files. Usually, you perform the high-level format with the standard DOS FORMAT program, using the following syntax:

FORMAT C: /S /V

This step high-level formats drive C (or volume C, in a multivolume drive), places the hidden operating-system files in the first part of this partition, and prompts for the entry of a volume label to be stored on the disk at completion.

The high-level format program performs the following functions and procedures:

1. Scans the disk (read only) for tracks and sectors marked as bad during the LLF, and notes these tracks as being unreadable.

2. Returns the drive heads to the first cylinder of the partition, and at that cylinder, head 1, sector 1, writes a DOS volume boot sector.

3. Writes a FAT at head 1, sector 2. Immediately after this FAT, it writes a second copy of the FAT. These FATs essentially are blank except for bad-cluster marks noting areas of the disk that were found to be unreadable during the marked-defect scan.

4. Writes a blank root directory.

5. If the /S parameter is specified, copies the system files (IBMBIO.COM and IBMDOS.COM or IO.SYS and MSDOS.SYS, depending on which DOS you run) and COMMAND.COM files to the disk (in that order).

6. If the /V parameter is specified, prompts the user for a volume label, which is written as the fourth file entry in the root directory.

Now DOS can use the disk for storing and retrieving files, and the disk is a bootable disk.


NOTE: The Format command can be run through the Windows Explorer within Windows 95 even on hard disks, as long as no files are open. You cannot format the drive where Windows 95 resides.

During the first phase of the high-level format, a marked defect scan is performed. Defects marked by the LLF operation show up during this scan as being unreadable tracks or sectors. When the high-level format encounters one of these areas, it automatically performs up to five retries to read these tracks or sectors. If the unreadable area was marked by the LLF, the read fails on all attempts.

After five retries, the DOS FORMAT program gives up on this track or sector and moves to the next. Areas that remain unreadable after the initial read and the five retries are noted in the FAT as being bad clusters. DOS 3.3 and earlier versions can mark only entire tracks bad in the FAT, even if only one sector was marked in the LLF. DOS 4 and later versions individually check each cluster on the track and recover clusters that do not involve the LLF marked-bad sectors. Because most LLF programs mark all the sectors on a track as bad, rather than the individual sector that contains the defect, the result of using DOS 3.3 or 4 is the same: all clusters involving sectors on that track are marked in the FAT as bad.


NOTE: Some LLF programs mark only the individual sector that is bad on a track, rather than the entire track. This is true of the IBM PS/2 low-level formatters on the IBM PS/2 Advanced Diagnostics or Reference disk. In this case, high-level formatting with DOS 4 or later versions results in fewer lost bytes in bad sectors, because only the clusters that contain the marked bad sectors are marked bad in the FAT. DOS 4 and later versions display the Attempting to recover allocation unit x message (in which x is the number of the cluster) in an attempt to determine whether a single cluster or all the clusters on the track should be marked bad in the FAT.

If the controller and LLF program together support sector and track sparing, the high-level format finds the entire disk defect-free, because all the defective sectors have been exchanged for spare good ones.

If a disk has been low-level formatted correctly, the number of bytes in bad sectors is the same before and after the high-level format. If the number does change after you repeat a high-level format (reporting fewer bytes or none), the LLF was not done correctly. The manufacturer's defects were not marked correctly; or Norton, Mace, PC Tools, or a similar utility was used to mark defective clusters on the disk. The utilities cannot mark the sectors or tracks at the LLF level; the bad-cluster marks that they make are stored only in the FAT and erased during the next high-level format operation. Defect marks made in the LLF consistently show up as bad bytes in the high-level format, no matter how many times you run the format.

Only an LLF or a surface-analysis tool can correctly mark defects on a disk; anything else makes only temporary bad-cluster marks in the FAT. This kind of marking may be acceptable temporarily, but when additional bad areas are found on a disk, you should run a new LLF of the disk and either mark the area manually or run a surface analysis to place a more permanent mark on the disk.

Hard Disk Drive Troubleshooting and Repair

If a hard disk drive has a problem inside its sealed HDA, repairing the drive usually is not feasible. If the failure is in the logic board, you can replace that assembly with a new or rebuilt assembly easily and at a much lower cost than replacing the entire drive.

Most hard disk problems really are not hardware problems; instead, they are soft problems that can be solved by a new LLF and defect-mapping session. Soft problems are characterized by a drive that sounds normal but produces various read and write errors.

Hard problems are mechanical, such as when the drive sounds as though it contains loose marbles. Constant scraping and grinding noises from the drive, with no reading or writing capability, also qualify as hard errors. In these cases, it is unlikely that an LLF will put the drive back into service. If a hardware problem is indicated, first replace the logic-board assembly. You can make this repair yourself and, if successful, you can recover the data from the drive.

If replacing the logic assembly does not solve the problem, contact the manufacturer or a specialized repair shop that has clean-room facilities for hard disk repair. (See Appendix B for a list of drive manufacturers and companies that specialize in hard disk drive repair.)

17xx, 104xx, and 210xxxx Hardware Error Codes

When a failure occurs in the hard disk subsystem at power-on, the Power-On Self Test (POST) finds the problem and reports it with an error message. The 17xx, 104xx, and 210xxxx errors during the POST or while running the Advanced Diagnostics indicate problems with hard disks, controllers, or cables. The 17xx codes apply to ST-506/412 interface drives and controllers; 104xx errors apply to ESDI drives and controllers; and 210xxxx errors apply to SCSI drives and host adapters.

Table 16.11 shows a breakdown of these error messages and their meanings.

Table 16.11  Hard Disk and Controller Diagnostic Error Codes

ST-506/412 Drive and Controller Error Codes
Error Description
1701 Fixed disk general POST error
1702 Drive/controller time-out error
1703 Drive seek error
1704 Controller failed
1705 Drive sector not found error
1706 Write fault error
1707 Drive track 0 error
1708 Head select error
1709 Error Correction Code (ECC) error
1710 Sector buffer overrun
1711 Bad address mark
1712 Internal controller diagnostics failure
1713 Data compare error
1714 Drive not ready
1715 Track 0 indicator failure
1716 Diagnostics cylinder errors
1717 Surface read errors
1718 Hard drive type error
1720 Bad diagnostics cylinder
1726 Data compare error
1730 Controller error
1731 Controller error
1732 Controller error
1733 BIOS undefined error return
1735 Bad command error
1736 Data corrected error
1737 Bad track error
1738 Bad sector error
1739 Bad initialization error
1740 Bad sense error
1750 Drive verify failure
1751 Drive read failure
1752 Drive write failure
1753 Drive random read test failure
1754 Drive seek test failure
1755 Controller failure
1756 Controller Error Correction Code (ECC) test failure
1757 Controller head select failure
1780 Seek failure; drive 0
1781 Seek failure; drive 1
1782 Controller test failure
1790 Diagnostic cylinder read error; drive 0
1791 Diagnostic cylinder read error; drive 1
SCSI Drive and Host Adapter Error Codes
096xxxx SCSI adapter with cache (32-bit) errors
112xxxx SCSI adapter (16-bit without cache) errors
113xxxx System board SCSI adapter (16-bit) errors
210xxxx SCSI fixed disk errors

The first x in xxxx is the SCSI ID number.
The second
x in xxxx is the logical unit number (usually 0).
The third
x in xxxx is the host adapter slot number.
The fourth x in xxxx is a letter code indicating drive capacity.

Most of the time, a seek failure indicates that the drive is not responding to the controller. This failure usually is caused by one of the following problems:

  • Incorrect drive-select jumper setting

  • Loose, damaged, or backward control cable

  • Loose or bad power cable

  • Stiction between drive heads and platters

  • Bad power supply

If a diagnostics cylinder read error occurs, the most likely problems are these:

  • Incorrect drive-type setting

  • Loose, damaged, or backward data cable

  • Temperature-induced mistracking

The methods for correcting most of these problems are obvious. If the drive-select jumper setting is incorrect, for example, correct it. If a cable is loose, tighten it. If the power supply is bad, replace it. You get the idea.

If the problem is temperature-related, the drive usually will read data acceptably at the same temperature at which it was written. Let the drive warm up for a while and then attempt to reboot it, or let the drive cool and reread the disk if the drive has overheated.


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