Absolute Beginners Guide to A+ Certification. Covers the Hardware and Operating Systems Exam

IDE/ATA Hard Disks

Integrated Drive Electronics ( IDE ) began to replace the older drive interfaces starting in the late 1980s and continues to be, by far, the most popular drive interface used today. IDE drives were originally used in systems designed for ST-412/506 hard drives , and some of their characteristics date back to the need to be compatible with old BIOSs.

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IDE was originally designed for hard drives, but several other types of storage devices can also be attached to it:

• Optical drives (including CD-ROM, CD-R, CD-RW, and all types of DVD drives)

• Removable-media drives, such as Zip, LS-120, LS-240, and others

• Tape backup drives

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These types of drives are referred to as AT Attachment Packet Interface ( ATAPI ) drives, and they use the same master / slave / cable select jumpers and 40-pin data cable as standard IDE drives do. The system BIOS on recent systems supports minimal functions for these drives, but software drivers are used to provide most functions. These devices should be installed on the secondary IDE channel, and hard drives should be installed on the primary IDE channel.

IDE/ATA Hardware Resources

The IDE/ATA hard disk interface, whether found on the motherboard or as an add-on card, uses the following resources. These resources are listed in Table 14.2.

Table 14.2. Standard Hardware Resource Use for IDE/ATA Hard Drive Interfaces

Each IDE hard drive interface, also known as an IDE channel , can operate two IDE drives. Therefore, systems with two IDE interfaces can operate up to four IDE drives.

EIDE and ATA Standards

Because the original IDE drives were developed as proprietary drive interfaces for use with brands such as Compaq and Zenith, the first IDE drives had major problems with compatibility and could not be autoconfigured by the BIOS.

Although it can still be difficult to "mix and match" some IDE drives from different vendors, a series of standards for IDE drives are referred to as the ATA specifications (AT Attachment). Table 14.3 provides an overview of the differences in the various ATA/IDE specifications.

Table 14.3. ATA/IDE Specifications and Features

An ATA-7 standard is currently in draft form. It is expected to provide standards for external hard drives and for the Ultra ATA-133 transfer rate (FastDrive; 133MBps) developed by Maxtor and available in current Maxtor drives.

Enhanced IDE is a marketing term used by some vendors to refer to the enhancements listed as ATA-2 in Table 14.3.

Serial ATA

Serial ATA ( SATA ) is a development of the ATA/IDE standard that provides a pathway to faster drives, greater reliability, and simpler installation than ATA/IDE.

Serial ATA uses a single seven-wire data cable, which uses high-speed serial technology instead of the parallel technology used by ATA/IDE to transmit signals between the drive and host adapter. Unlike ATA/IDE drives, SATA drives use a direct one-to-one connection between the drive and the host adapter. Thus, no jumpers are necessary to configure the drive. Hooray!

Serial ATA uses the same commands as ATA/IDE, so SATA drives and host adapters can be retrofitted to existing systems. SATA drives can be prepared by Windows 98 and more recent versions. Some recent systems include one or more SATA host adapters on the motherboard. On such systems, after the SATA host adapter is enabled in the system BIOS, SATA drives are configured just as ATA/IDE drives are.

The original version of SATA, SATA-150, has a maximum data transfer rate of 150MBps. Faster versions are expected in the future.

ATA RAID Types

RAID (redundant array of inexpensive drives) is a method for creating a faster or safer single logical hard disk drive from two or more identical physical drives. RAID arrays have been common for years on servers using SCSI-interface drives. However, a number of recent systems feature ATA RAID or SATA RAID host adapters on the motherboard. ATA and SATA RAID host adapter cards can also be retrofitted to systems lacking onboard RAID support.

ATA and SATA RAID types include the following:

• RAID Level 0 Two drives are treated as a single drive, with both drives used to simultaneously store different portions of the same file. This method of data storage is called striping. Striping boosts performance, but if either drive fails, all data is lost. Don't use striping for data drives.

• RAID Level 1 Two drives are treated as mirrors of each other; changes to the contents of one drive are immediately reflected on the other drive. This method of data storage is called mirroring. Mirroring provides a built-in backup method and provides faster read performance than a single drive. Suitable for use with program and data drives.

• RAID Level 0+1 Four drives combine striping plus mirroring for extra speed plus better reliability. Suitable for use with program and data drives.

Most motherboards support only RAID 0 and RAID 1. Some host adapters support RAID 0, 1, and 0+1.

ATA or SATA RAID host adapters can sometimes be configured to work as normal ATA or SATA host adapters. Check the system BIOS setup or add-on card host adapter setup for details.

ATA and Serial ATA Cabling

ATA/IDE drives use one of two types of cables, depending upon their speed, whereas Serial ATA drives use one type of cable:

• ATA drives that support PIO modes or Ultra DMA (UDMA) 33 transfer rates can use a 40-wire, 40-pin cable. This is a straight-through cable; master and slave assignments are determined by drive jumpers.

• ATA drives that support UDMA-66 or faster transfer rates must use an 80-wire, 40-pin cable. The connector is the same as the original ATA/IDE cable, but the additional 40 wires are used to provide an electrically cleaner signal. The position of the drives on the cable along with drive jumpers are used to determine master and slave assignments. (See "Drive Jumpers and Cable Select," later in this chapter, for details.) Many of these cables are color coded. In such cases, the blue connector is used for the host adapter, the gray connector is used for the slave drive, and the black connector is used for the master drive.

• SATA drives use a seven-pin cable. No jumpers are used by SATA drives; each drive connects directly to an SATA port on the host adapter or motherboard, so SATA doesn't use master or slave settings.

Figure 14.7 compares these cables to each other. Note the ridged appearance of the 40-wire ATA/IDE cable compared to the smoother 80-wire cable; the 40-wire cable uses thicker wires.

IDE Data Cable Keying Standards

Depending upon the design of the ATA/IDE cable and connectors used in a particular system, you might discover difficulties in properly connecting devices:

• Some IDE cables have a raised projection in the middle of the cable connector, which is designed to correspond to a cutout on the IDE drive or host adapter shield around the connector pins. The cables in Figure 14.8 use this keying method.

  Figure 14.8. Two typical ATA/IDE drives configured for cable select. Some drives, such as the one on the left, require the user to consult a chart on the drive's top plate or in the system documentation for correct settings, whereas others silk-screen the jumper settings on the drive's circuit board.

• Some IDE cable connectors plug the hole for pin 20 and are designed to be used with IDE drives or host adapters that omit pin 20. The cables in Figure 14.8 also support this keying method.

• Some IDE cable connectors don't use either method, making it easy to attach the cable incorrectly. Many vendors continue to use this type of cable because manufacturers can't agree on which of the positive keying methods listed previously should be standard.

Drive Jumpers and Cable Select

With two drives possible per ATA/IDE cable, the ATA/IDE interface uses one of two methods to determine which drive is master and which is slave:

• Drives connected to the 40-pin, 40-wire cable use the master and slave jumper settings shown in Figure 14.9.

  Figure 14.9. A typical adapter kit for a 3.5-inch drive. Screw a attaches the frame at hole #1; screw b attaches the frame at hole #2, with corresponding attachments on the opposite side of the drive and frame. Drive rails used by some cases can be attached to the adapter kit.

• Drives connected to the 40-pin, 80-wire cable required by UDMA-66 and faster transfer rates use the cable select jumper setting shown in Figure 14.9 along with the position of the drive on the cable: master on black connector, slave on gray connector, and blue connector to host adapter.

Four different jumper positions are available on the bottom or rear of a typical IDE hard drive:

• One drive installed: Use master jumper or don't jumper any pins (varies by model).

• Master drive installed with slave; jumper drive as master.

• Slave drive; jumper drive as slave. Normally, this is used only when two drives are attached to the IDE cable.

• 80-wire cable in use : Jumper both drives as cable select and connect drives to the appropriate connectors for master and slave.

Figure 14.8 shows two ATA/IDE hard drives configured for cable select.

The Cap Limit jumper shown in Figure 14.8 is used only on systems that cannot use the drive at full capacity.

ATA/IDE Hard Drive Physical Installation

The following steps apply to typical ATA/IDE drive installations. If you are installing an ATAPI drive, you might use a 5.25-inch bay, but the other steps will be the same.

1. Open the system and check for an existing 3.5-inch drive bay; use an internal bay if possible.

2. If a 3.5-inch drive bay is not available but a 5.25-inch drive bay is, attach the appropriate adapter kit and rails as needed, as shown in Figure 14.9.

3. Jumper the drive according to the cable type used: 40-wire cables use master and slave; 80-wire cables use cable select or master and slave.

4. Attach the appropriate connector to the drive, making sure to match the colored marking on the edge of the cable to the end of the drive connector with pin 1. Pin 1 might be marked with a square solder hole on the bottom of the drive or silk-screening. If no markings are visible, pin 1 is usually nearest the drive's power connector. Disconnect the cable from the host adapter or other ATA/IDE drive if necessary to create sufficient slack .

   Move the jumper simply by grasping it with a pair of tweezers or small needlenose pliers and gently pulling straight backward. It's always best to change jumper settings before inserting the drive into the PC because they can be especially difficult to reach after the drive is installed.

5. Slide the drive into the appropriate bay and attach as needed with screws or by snapping the ends of the rails into place.

6. Attach the power connector; most IDE hard drives use the larger four-wire (Molex) power connector originally used on 5.25-inch floppy disk drives. Use a Y-splitter to create two power connectors from one if necessary.

7. Reattach the data cable to the other ATA or ATAPI drive and host adapter if necessary.

8. Change the jumper on the other ATA or ATAPI drive on the same cable if necessary. For example, Western Digital does not use a jumper to indicate a single drive is installed on the cable. Instead, the jumper block is removed, or might be stored across pins that are not used to set the drive's configuration. The Master setting is used only when two drives are on the cable. For example, if you are adding a slave drive to a cable with one drive already attached, you might need to adjust the jumper on the existing drive from single (no jumper) to master. Refer to Figure 14.8.

9. Verify correct data and power connections to IDE drives and host adapters.

10. Turn on the system and start the BIOS configuration program.

Figure 14.10 shows a typical ATA/IDE drive before and after power and data cables are attached.

SATA Hard Drive Physical Installation

The process of installing an SATA drive differs from that used for installing an ATA/IDE drive because there are no master or slave jumpers and the SATA data cable goes directly from host adapter to drive. The following instructions assume the system already has an onboard or add-on card SATA host adapter already installed. If you need to install an SATA host adapter, see the next section for details.

1. Open the system and check for an existing 3.5-inch drive bay; use an internal bay if possible.

2. If a 3.5-inch drive bay is not available but a 5.25-inch drive bay is, attach the appropriate adapter kit and rails as needed, as shown previously in Figure 14.9.

3. Attach the SATA cable to the drive; it is keyed so it can only be connected in one direction.

4. Slide the drive into the appropriate bay and attach as needed with screws or by snapping the ends of the rails into place.

5. Attach the power connector; use the adapter provided with the drive to convert a standard Molex connector to the edge connector type used by SATA. If the drive didn't include a power connector, purchase one.

6. Attach the data cable to the host adapter.

7. Verify correct data and power connections to IDE drives and host adapters.

8. Turn on the system and start the BIOS configuration program if the SATA host adapter is built into the motherboard. Enable the SATA host adapter, save changes, and restart your system.

9. If the SATA drive is connected to an add-on card, watch for messages at startup indicating the host adapter BIOS has located the drive.

10. Install drivers for your operating system to enable the SATA drive and host adapter to function when prompted. See Chapter 15, "Preparing Hard and Floppy Drives with Windows," for details.

Figure 14.11 shows a typical SATA drive. Figure 14.12 shows typical ATA/IDE and SATA host adapter connections on a recent motherboard.

Installing an SATA Host Adapter

Most systems don't include an SATA host adapter on the motherboard. Thus, to add an SATA drive to many systems, you will also need to install an SATA host adapter card such as the one pictured in Figure 14.13. Follow this procedure:

1. Shut down the system and disconnect the power cable from the outlet to cut all power to the system.

2. Use ESD protection equipment, such as a wrist strap and work mat, if available. (See Chapter 13, "Safety and Recycling," for details.)

3. Open the computer and locate an unused PCI slot.

4. After removing the slot cover, insert the SATA card into the slot. See Chapter 2, "PC Anatomy 101," for basic instructions on adding expansion cards, such as the SATA host adapter described here.

5. Secure the card into place with the screw removed from the slot cover.

6. Connect the card to the SATA drive with an SATA data cable. The cable might be provided with the card or with the drive.

7. Reconnect the power cord and restart the computer.

8. Install drivers when prompted.

9. Restart your computer if prompted.

10. Open the Windows Device Manager to verify that the SATA host adapter is working. It should be listed under the category SCSI Controllers, SCSI Adapters, or SCSI and RAID Controllers (see Figure 14.13).

BIOS Configuration

For ATA/IDE and SATA drives controlled by the motherboard BIOS, the following information must be provided:

• Hard drive geometry

• Data transfer rate

• LBA translation

Hard drive geometry refers to several factors used to calculate the capacity of a hard drive. These factors include the following:

• The number of sectors per track

• The number of read/write heads

• The number of cylinders

The surface of any disk-based magnetic media is divided into concentric circles called tracks . Each track contains multiple sectors. A sector contains 512 bytes of data, and is the smallest data storage area used by disk drives.

Each side of a hard disk platter used for data storage has a read-write head that moves across the media. There are many tracks on each hard disk platter, and all the tracks on all the platters are added together to obtain the cylinder count.

Figure 14.14 helps you visualize sectors, tracks, and cylinders.

Before the drive can be prepared by the operating system, it must be properly identified by the system BIOS.

Depending on the age of the system and the size of the ATA/IDE hard drive, there are two different methods used for configuring an ATA/IDE or SATA drive:

• Manual entry of IDE parameters

• Auto-detection of the IDE hard drive type

Manual Entry of IDE Parameters

This feature started to become common in the BIOS configuration program around 1990, and virtually all systems still allow this today. Systems with this feature have a user-defined drive type that enables you to manually enter the correct cylinders, heads, sectors per track, and special configuration information.

This information is not stored in the BIOS itself, but rather in the CMOS memory, which can be lost due to battery failure or other problems.

Today, this method of defining the hard disk geometry is used primarily when a drive that was prepared using a different disk geometry than that recommended by the manufacturer is being reinstalled in a system or is being moved to another system.

Auto-detection of the IDE Hard Drive Type

Auto-detection is a variation on the user-defined drive type. Auto-detection was developed in the early 1990s, enabling the BIOS to query the drive for the correct configuration information. This information also is placed in the user-defined drive type and stored in the CMOS memory (see Figure 14.15).

Auto-detection is the best way to install a new ATA/IDE or SATA drive because other settings such as LBA translation, block mode (multi-sector transfers), and UDMA transfer rates will also be configured properly.

Some BIOSs perform the automatic detection of the drive type every time you start the system by default. Although this enables you to skip configuring the hard drive setting, it also takes longer to start the system and prevents the use of nonstandard configurations for compatibility reasons.

To save time during the boot process and to allow you to see the actual values used for the drive in the system BIOS, you can use these methods:

• Detect the drive with the BIOS setup program.

• Configure the drive's geometry values manually by entering the manufacturer-supplied values into a user-defined drive type. Then, record the values on a sticker attached to the outside of the drive or the system unit in case the CMOS memory is corrupted and the data must be re-entered.

Depending on the system, removable-media ATAPI (ARMD) drives such as Zip and LS-120 should be configured as Not Present or Auto in the system BIOS setup or as ARMD drives depending upon the BIOS options listed. These drives do not have geometry values to enter in the system. The CD-ROM setting should be used for ATAPI CD-ROM and similar optical drives, such as CD-R, CD-RW, and DVD. Using the correct BIOS configuration for ATAPI drives will enable them to be used to boot the system on drives and systems that support booting from ATAPI devices.

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Creating an ATA or SATA RAID Array

An ATA or SATA RAID array generally requires

• Two or more identical drives Some systems enable a single drive to be converted into an array, but this is not recommended. If one drive is larger than the other, the additional capacity will be ignored.

• A RAID-compatible motherboard or add-on host adapter card Both feature a special BIOS, which identifies and configures the drives in the array.

Because RAID arrays use off-the-shelf drives, the only difference in the physical installation of drives in a RAID array is where they are connected. They must be connected to a motherboard or add-on card that has RAID support.

After the drive(s) used to create the array are connected to the RAID array's host adapter, restart the computer. Start the system BIOS setup program and enable the RAID host adapter if necessary. Save changes and exit the BIOS setup program.

After enabling the RAID array host adapter, follow the vendor instructions to create the array. Generally, this requires you to activate the RAID array setup program when you start the computer and follow the prompts to select the type of array desired. After the RAID array is configured, the drives are handled as a single physical drive by the system.

Overcoming Hard Disk Capacity Limitations with LBA Mode

When the IDE interface was developed, several limitations on the total capacity of an IDE hard disk existed:

• MS-DOS limitation of 1,024 cylinders per drive

• IDE limitation of 63 sectors per track

• BIOS limitation of 16 heads

These limitations resulted in a total capacity of 504MiB, or approximately 528 million bytes. By 1994, these limitations were no longer theoretical; users were able to purchase drives that exceeded this size and a BIOS-based way was needed to ensure reliable access to the drives' full capacity.

Previously, systems that were incapable of using the entire capacity of a drive would use a software driver such as OnTrack's Disk Manager, but this approach could be risky to data if the driver or special drive configuration failed.

The most common method for enabling larger IDE hard drives to be used is called Logical Block Addressing ( LBA ) . How does LBA work?

LBA mode alters how the drive is accessed internally. It increases the BIOS limit to 255 heads and works around the MS-DOS limitation of 1,024 cylinders per drive by dividing the cylinders and multiplying the heads by the same factor. Thus, an LBA mode drive has the same capacity as a non-LBA mode drive, but its configuration is different.

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For example, assume an ATA/IDE hard drive has a factory-defined configuration of 13,328 cylinders, 15 heads, and 63 sectors per track. To determine the drive capacity, multiply the cylinders by the heads by the sectors per track. Divide the result by 2,048, and the capacity is 6.15GiB (about 6.4GB). However, if you don't enable LBA mode, only the first 1,024 cylinders are recognized by the system, shrinking the drive to 504MiB (528MB).

Which of the three values listed previously is the problem? The cylinder count! When LBA mode is enabled, the following changes take place in the logical geometry of the drive:

• The cylinder count is divided by 15 (13,328/15=888.53rounded up to 889).

• The head count is multiplied by 15 (15x15=225).

Both of these new logical values fall below the BIOS limits adjusted by LBA. Consequently, the 6.4GB drive is recognized at full capacity. That's a pretty good trick!

Remember, every operating system with a Microsoft logofrom dusty old MS-DOS to the latest Windows versionis incapable of using more than 504MiB of any IDE/ATA or SATA hard drive unless LBA mode is enabled (SCSI has the same limitation, but it's handled a different way).

It's Not Nice to Fool Around with LBA!

If LBA mode is disabled after a drive has been prepared using LBA mode, the drive will not work properly, to put it mildly.

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With MS-DOS, the system at some point might try to write to data stored on areas past the barrier of 1,024 cylinders that LBA mode overcomes. Without LBA mode to translate the drive's full capacity, the system will loop back to the beginning of the drive and overwrite the partition table and file allocation table, destroying the drive's contents. Ouch!

If you're running Windows (all 99.9% of you), don't panic. Windows won't boot if you turn off LBA mode, but you won't lose any data.

If you're the paranoid type (did I enable LBA mode?), you can use your operating system's disk preparation software to find out if LBA is working. See Chapter 15 for details.

Additional Drive-Size Limitations

Early versions of LBA-mode BIOS could not handle drives of more than 4,095 cylinders (approximately 2.1GB); many more recent systems cannot handle drives with more than 16,384 cylinders (approximately 8.4GB). Support for drives with more than 16,384 cylinders, referred to as Extended INT13h or EBIOS support, also requires support in the operating system (Windows 95 or later).

Whenever possible, you should install a system BIOS upgrade to handle limitations of these types. Check out Chapter 6, "BIOS and CMOS Configuration," for the details. If a BIOS upgrade is not available for your system, you can install an ATA host adapter card with an auxiliary BIOS onboard. The BIOS chip on the card can override your existing BIOS to provide the additional support necessary to operate the hard drive at full capacity. An ATA host adapter card is installed using a process similar to that used to install an SATA host adapter card. Like the SATA card, it uses an empty PCI slot.

The upgrade version of Windows 95 and the original OEM version cannot use drives larger than 8.4GB because they use the file system (FAT16) inherited from MS-DOS. The OSR 2.x (Windows 95B/C) versions can use drives up to 32GB in size. Later versions of Windows can use drives over 32GB in size. For more details, see Chapter 15.

ATA/IDE Performance Optimization

If your hard drive is stuck in first gear, so is your system. Fortunately, most systems that support LBA mode also offer several different ways to optimize the performance of IDE drives and devices. These include

• Selecting the correct PIO or DMA transfer mode in the BIOS

• Selecting the correct block mode in the BIOS

• Installing busmastering Windows drivers

• Enabling DMA mode in Windows

• Adjusting disk cache software settings

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PIO and DMA Transfer Modes

IDE hard drives are capable of operating at a wide variety of transfer speeds. Depending on when the drive was built, IDE hard drives are designed to run in one of two modes:

• PIO (Programmed Input/Output) mode

• Ultra DMA (UDMA) mode (also called Ultra ATA mode)

These modes refer to different peak transfer rates the hard drive can achieve. Some systems automatically determine the correct transfer rate, whereas others require you to select the correct speed from a list of options. Selecting transfer rates too fast for the drive can cause data corruption, and selecting rates that are too low can slow down the system.

To achieve a given transfer rate, the hard disk, the host adapter (card or built-in), and the data cable must be capable of that rate. In addition, the host adapter must be configured to run at that rate.

Tables 14.4 and 14.5 list the most common transfer rates. Check the drive documentation or with the drive vendor for the correct rating for a given drive.

Table 14.4. PIO Peak Transfer Rates

Although PIO modes 3 and 4 require a fast 32-bit IDE interface, not every VL-Bus card is capable of such transfer rates; some require software drivers to achieve mode 3/mode 4 speeds. Check the documentation for the host adapter card or the BIOS configuration screen for systems using a built-in ATA/IDE interface to find out which speeds are supported.

Table 14.5. UDMA (Ultra ATA) Peak Transfer Rates

These modes are backward compatible, enabling you to select the fastest available mode if your system lacks the correct mode for your drive. ATA/IDE drives are backward compatible; you can select a slower UDMA mode than the drive supports if your system doesn't support the correct UDMA mode, or you can use PIO modes if your system has no UDMA options in the BIOS. Performance will be slower, but the drive will still work.

Note that UDMA 4 (UDMA-66) and faster modes require the use of a 40-pin, 80-wire cable previously shown in Figure 14.9. If a 40-wire cable is used, UDMA 2 (UDMA-33) is the fastest speed possible.

IDE Block Mode

IDE block mode refers to an improved method of data handling. Originally, a hard drive was allowed to read only a single 512-byte sector before the drive sent an IRQ to the CPU. Early in their history, some IDE hard drives began to use a different method called block mode, which enabled the drive to read multiple sectors, or blocks, of data before an IRQ was sent. Virtually all recent drives support block mode. Enable it (also called multisector transfers, as shown in Figure 14.16) in the system BIOS to get the performance expected from the drive.

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Most recent systems automatically determine block mode capability when they auto-detect the drive. Others require that you enable or disable block mode manually, and still others enable you to select the number of blocks the drive can read. Some very old ATA/IDE drives do not support block mode and run more slowly when it is enabled. If you must set block mode manually, check with the drive vendor to see whether the drive supports block mode and what options to select if it does.

IDE Busmastering Drivers

A third way to improve IDE hard disk performance is to install busmastering drivers for the IDE host interface. A busmaster bypasses the CPU for data transfers between memory and the hard disk interface. This option is both operating system specific and motherboard/host adapter specific.

Only systems running Windows 9x and newer versionsbut not MS-DOS, Windows NT 3.51, or Windows NT 4.0 before Service Pack 3can use busmastering drivers. Most newer systems have motherboards that support busmastering drivers. Check with the motherboard or system vendor for busmastering information.

Busmastering drivers require special support from the motherboard's chipset. The original retail versions of Windows 95 and Windows NT 4.0 don't include busmastering drivers (get them from the motherboard or motherboard chipset vendor), but Windows 95 OSR 2.x (also called Windows 95B), Windows 98, and newer versions include busmastering support for motherboards with the correct Intel chipsets. Motherboards using other chipsets might require that you download the correct driver from the motherboard vendor if you are using Windows 95 OSR 2.x; Windows 98 and newer versions include busmastering drivers for major non-Intel chipsets. In most cases, you must manually install the correct driver. If your motherboard includes a driver CD, it might contain more up-to-date busmastering drivers than those included with Windows.

Because busmastering bypasses the CPU, be sure you are installing the correct drivers. Carefully read the motherboard or system vendor's instructions. You might not be able to use busmastering drivers if you use a CD-R or CD-RW drive connected to the IDE interface. In such cases, use the regular IDE host adapter driver supplied with Windows.

Enabling DMA Transfers for IDE Devices in Windows

All versions of Windows from Windows NT 4.0 (Service Pack 3 and greater) and Windows 95 up through Windows XP enable the user to allow DMA transfers between ATA/IDE devices and the system. DMA transfers bypass the CPU for faster performance and are particularly useful for optimizing the performance of both hard drives and optical drives, such as high-speed CD-ROM drives and DVD drives.

Follow this procedure to enable DMA transfers for a particular IDE device in Windows 9x/Me:

1. Open the System Properties sheet. Right-click My Computer and select Properties, or open the Control Panel and select System.

2. Click Device Manager.

3. Click the plus sign (+) next to the Disk Drives category (for hard drives) or CDROM (for CD-ROM, CD-R/CD-RW, or DVD drives).

4. Click the drive for which you want to enable DMA transfers, and click Properties. Standard IDE hard drives are listed as Generic; other devices and CD-ROM/optical drives are listed by name .

5. Click Settings.

6. Click the DMA box to put a check mark next to DMA.

7. Click OK.

8. Restart the computer as prompted.

Repeat this procedure for each IDE device.

With Windows 2000/XP, follow this procedure:

1. Open the System Properties sheet. Right-click My Computer and select Properties, or open the Control Panel and select System.

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   Before enabling DMA or UDMA mode, check the documentation for the drive to see if it supports this mode. Enabling DMA or UDMA on a drive that does not support it can have disastrous effects. If the drive can't go faster than UDMA 2 although it's rated for higher speeds (see Figure 14.16), you might want to change the cable. You need the 80-wire cable shown earlier in Figure 14.8 to get to UDMA 4 (66MBps) or faster transfer rates. It's also okay to use the 80-wire cable for slower speeds. Figure 14.18. A wide (68-pin) SCSI ribbon cable (left) compared to a narrow (50-pin) SCSI ribbon cable (right).

2. Click Hardware, Device Manager.

3. To determine which drives are connected to which host adapter, open the category containing the drives (Disk Drives for hard or removable-media drives or DVD/CD-ROM Drives for optical drives) and double-click the drive to open its Properties sheet. The location value visible on the General tab shows to which host adapter and device number the drive is connected. For example, location 0 (1) indicates the drive is connected to the primary host adapter (0) as the secondary device (1).

4. Click the plus sign next to the IDE ATA/ATAPI Controllers category.

5. Double-click the host adapter for which you want to adjust properties (primary or secondary IDE channel) to open its Properties sheet.

6. Click Advanced Settings.

7. To enable DMA for a particular drive, select DMA if available for the Transfer mode. To disable DMA, select PIO only (see Figure 14.16).

8. Click OK.

9. Restart the computer as prompted.

If DMA is not available, you might need to install the correct busmastering driver for your system.

Adjusting Disk Caching Settings in Windows

Disk caches use a portion of memory to hold information flowing to and from disk drives. The system accesses the cache memory before accessing the main memory. If the information on disk is already in the cache memory, it is accessed far more quickly than if it were read from disk.

Disk cache software is incorporated into Windows 9x and newer Windows versions. (MS-DOS and Windows 9x also include the Smartdrv.exe disk cache program for use at a command prompt.)

The disk cache in Windows 9x and newer versions automatically adjusts to increases in physical RAMas more RAM is added, the amount of RAM used for disk caching increases. The disk cache also varies in sizethe amount of RAM used for disk caching varies with system activity. Windows uses two types of disk caching:

• Write-behind caching This uses the disk cache for both disk reads and disk writes . This frees up an application saving data to disk to proceed to the next task.

• Read-only caching This uses the disk cache for disk reads only. Disk writes go to the drive and cause delays with some applications.

By default, Windows uses write-behind caching for hard drives and read-only caching for floppy, removable-media, and CD-ROM/optical drives.

You can alter Windows 9x and Me's disk-caching settings by following this procedure:

1. Open the System Properties sheet. Right-click My Computer and select Properties, or open the Control Panel and select System.

2. Click Performance.

3. Click File System.

4. Select options as directed next.

To enable Windows to use disk caching for hard drives most effectively, perform the following steps:

1. Select Hard Disk.

2. Select Network Server from the Typical role of this computer menu.

3. Drag the Read-Ahead Optimization selector to Full.

To enable write-behind caching for floppy and other removable disk drives, follow this procedure:

1. Click Removable Disk.

2. Click Enable Write-Behind Caching.

You must make sure all data has been saved to the disk before removing it.

To maximize caching for CD-ROM drives, follow this procedure:

1. Click CD-ROM.

2. Drag the Supplemental Cache Size selector to Large.

3. Select Quad-Speed or Higher from the Optimize Access Pattern menu.

You can disable write-behind disk caching by following this procedure (recommended for troubleshooting only because it slows down the system significantly):

1. Click Troubleshooting.

2. Click Disable Write-Behind Caching.

To complete the changes, click OK and restart the system when prompted.

To adjust disk-cache settings for Windows 2000/XP, follow this procedure:

1. Open the System Properties sheet and click Advanced.

2. Click the Settings button in the Performance section.

3. Click Advanced.

4. Click System Cache to use more memory on a computer that provides server features to other computers or to improve overall disk-caching performance. To avoid reducing system performance, you should enable this feature only on systems with 512MB of RAM or more.

5. Click OK and restart the system as prompted.