
A H - 2 8 0    WESTERN DIGITAL
NO MORE PRODUCED                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 2.5"/SUPERSLIMLINE    Cylinders    1390|  980|     |
Capacity form/unform    86/      MB        Heads           4|   10|     |
Seek time   / track  16.0/ 5.0 ms          Sector/track     |   17|     |
Controller           IDE / AT              Precompensation
Cache/Buffer            32 KB SEGMENTED    Landing Zone
Data transfer rate    1.250 MB/S int       Bytes/Sector      512
                      4.500 MB/S ext
Recording method     RLL 2/7                        operating  | non-operating
                                                  -------------+--------------
Supply voltage     5 V          Temperature *C         5 55    |    -40 65
Power: sleep          0.5 W     Humidity     %         8 85    |      5 95
       standby        0.5 W     Altitude    km            2.600|        12.000
       idle           1.3 W     Shock        g        10       |    100
       seek               W     Rotation   RPM      3383
       read/write     2.4 W     Acoustic   dBA        36
       spin-up            W     ECC        Bit   56
                                MTBF         h     100000
                                Warranty Month        24
Lift/Lock/Park     YES          Certificates     CSA,FCC,IEC950,UL1950,VDE    

**********************************************************************
                        L   A   Y   O   U   T
**********************************************************************
WESTERN  WDAB130/AB140/AH260/AH280  TECHNICAL REFERENCE MANUAL








  ---+43---------------J1-----------------------1---7-5-3-1-+-----
     |o o o o o o o o o o o o o o o o o o o o o o . o o o o |J2
     |o o o o o o o o o o o o . o o o o o o o o o . o o o o |
     44----------------------20-----------------2---8-6-4-2-+










**********************************************************************
                      J   U   M   P   E   R   S
**********************************************************************
WESTERN  WDAB130/AB140/AH260/AH280  TECHNICAL REFERENCE MANUAL

 Jumper Setting
 ==============

 Single Drive
 ------------
             --+7-5-3-1+
               |o o o o|
               |o o o o|  J2
             --+8-6-4-2+

 The drive have a jumper block (J2 located next to the 44-pin
 connector on the drive. If you are installing the drive as the only
 intelligent drive in the system, you do not need to install jumpers
 on the J2 connector. This is considered a standard single drive
 installation, and no jumpers are required. Note that even with no
 jumper installed, the drive checks the DRIVE ACTIVE/SLAVE PRESENT
 (DASP) signal to determine if a slave intelligent drive is present.


 Dual Installation
 -----------------
 If you have a dual installation (two intelligent drives), you must
 designate one of the drives as the master and the other as the slave
 drive. The jumper pins on the J2 connector need to be configured for
 the dual installation.


 Master Drive
 ------------

             --+7-5-3-1+
               |o o X o|   J2
               |o o X o|
             --+8-6-4-2+

 To designate the drive as the master, place a jumper shunt on pins
 3-4. When configured as the master drive, the drive assumes that a
 slave drive is present. The jumper on pins 3-4 is optional if the
 slave drive follows the same protocol (Common Access Method AT Bus
 Attachment) as the master.

 Dual installations require a master/slave drive configuration, where
 one drive is designated as the primary (master) drive and the other
 is designated as the secondary (slave) drive. The drives are
 compatible in dual installations with other intelligent drives that
 support a master/slave configuration.


 Slave Drive
 -----------

             --+7-5-3-1+
               |o o o X|
               |o o o X|   J2
             --+8-6-4-2+

 To designate the drive as a slave, place a jumper shunt on pins 1-2.
 When configured as the slave drive, the drives delay spin up for four
 seconds after powerup reset. This feature prevents overloading of the
 power supply during powerup.


 Reserved
 --------
             --+7-5-3-1+       --+7-5-3-1+
               |o X o o|         |X o o o|
               |o X o o|  J2     |X o o o|  J2
             --+8-6-4-2+       --+8-6-4-2+



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                      I   N   S   T   A   L   L
**********************************************************************
WESTERN  WDAB130/AB140/AH260/AH280  TECHNICAL REFERENCE MANUAL

 Notes on Installation
 =====================

 Orientation
 -----------
 The drives can be mounted in many different ways depending upon the
 physical design of your system.


 Screw Size Limitations
 ----------------------
 The drive is mounting to the chassis using four M3 x .5-6H screws
 from the bottom or from the side.

 Caution: Screws which are too long will damage board components. The
 side mounting screws must engage no mre than .125 inch. The bottom
 mounting screws must engage no more than .17 inch.


 Connector
 ---------
 The drives connect directly to an industry-standard 44-pin IDE Inter-
 face connector.


 Intelligent Drive
 -----------------
 The drives do not require a slot-mounted controller card since the
 controller circuitry and 44-pin connector are already mounted on the
 drive.


 Grounding
 ---------
 The mounting screws connect the head disk assembly and the printed
 circuit board to the system chassis ground. Therefore, no external
 grounding strap is required.



**********************************************************************
                      F   E   A   T   U   R   E  S
**********************************************************************
WESTERN  WDAB130/AB140/AC260/AC280  TECHNICAL REFERENCE MANUAL

 General Description
 -------------------
 Western Digital's Tidbit I Series and Tidbit II Series drives are
 high-performance, 2.5-inch intelligent drives for portable, AT-
 compatible personal computers.

 The Tidbit I and II drives include advanced, reduced-power operating
 modes to extend battery life. The drives have an average seek time of
 sub-16ms, and including CacheFlow(TM), Western Digital's adaptive,
 multi-segmented, 32-Kbyte caching system. CacheFlow constantly
 evaluates the size of the data request and the type, whether random
 or repetitive, and adapts to the optimum caching method to provide
 maximum system throughput.


 Automatic Head Parking
 ----------------------
 Head parking is automatic. On powerdown, the drive heads retract to
 safe, non-data landing zone and lock into position, thus protecting
 data integrity.


 Preparing the Drive for Use
 ---------------------------
 The drives are preformatted (low-level) at the factory and come
 equipped with a full complement of defect management characteristics.
 No modifications are required before installation. If at some later
 time you need to perform defect mapping, contact Western Digital
 Technical Support for information on the WDAT_IDE utility management.


 Embedded Sector Servo Control
 -----------------------------
 These drives feature an embedded sector servo concept to provide
 sampled, position feedback information to the head position servo
 system. The embedded information precedes each data sector and
 provides position updates on a sector by sector basis. This high
 sampling rate supports the high-frequency servo bandwidth required
 for fast access times as well as highly accurate generation of servo
 feedback information without requiring the full data surface
 required by a dedicated servo control concept.


 Translation
 -----------
 The drives provide a linear disk address translator to convert
 logical sector addresses to physical sector addresses to ensure
 compatibility with any drive setup parameter.


 Error Recovery
 --------------
 The drives use a 56-bit Error Correction Code (ECC) for automatic
 detection and correction of errors in the data field.


 Guaranteed Compatibility
 ------------------------
 Western Digital performs extensive testing in its Functional
 Integrity Testting Labs (FIT Lab(TM)) to ensure compatibility to all
 AT-compatible computers and standard operating systems.


 Zoned Recording
 ---------------
 The drives employ zoned recording to increase the data density on the
 outer tracks of the drive. The outermost tracks contain 40 percent
 more sectors than the innermost tracks, thereby increasing the total
 capacity of the drive.


 Buffer RAM
 ----------
 A 32-Kbyte static RAM buffer enhances data throughput by buffering
 sector data between the drive electronics and the system bus. The RAM
 only buffers read/write data and ECC information. The buffer is
 accessed by two channels, each having a separate 15-bit address and
 byte-count register. The channels operate simultaneously, accepting
 read and write operations from two data paths. The address access
 time for the buffer RAM is 120 ns (maximum).


 Air Filtration System
 ---------------------
 It is absolutely essential that air circulating within the drive be
 particle free. The HDA is assembled in a Class 100 purified air
 environment, and then sealed with tape. To retain this clean
 environment, the drive is equipped with two filters. One filter, the
 recirculating filter, cleans the air within the HDA. The
 recirculating filter traps any particulates which may be generated
 during spindle start and stop operations. Mounting the recirculating
 filter next to the disk places the filter in the direction of the air
 flow. This strategic placement of the filter allows the rotating
 disks to act as an air pump forcing air through the recirculating
 filter. A second filter, the breather filter, cleans any external air
 entering the HDA. The breather filter also equalizes the internal and
 external air pressure. The breather filter is located on the bottom
 of the HDA.


 Defect Management
 -----------------
 Every drive undergoes factory-level intelligent burn-in, which
 troughly tests for any defective sectors on the media before the
 drive leaves the manufacturing facility. Following he extensive
 tests, a primary defect list is created. This list contains the
 sector, cylinder, and head numbers for all defects. The purpose of
 the sector/track map is to manage the reallocation of spare sectors
 and tracks after they have been assigned.


 Translation
 -----------
 The drives implement linear address translation. The translation mode
 and translated drive configuration are selected by using the Set
 Drive Parameters command to issue head and sector/track counts to the
 translator. The product of the cylinder, head, and sector/track
 counts must be equal to or less than the maximum number of sectors
 available to the user. The maximum number of sectors per drive for
 the AB130 and AB140 drives are 63,475 and 83,564 sectors,
 respectively. The maximum number of sectors per drive for the AH260
 and AH280 are 123,546 and 167,130 sectors, respectively. Each sector
 consists of 512 bytes.

 The minimum value for any translation parameter is one. The maximum
 value for any translation parameters is as follows:

 Sector/track (SPT) 63
 Heads              16
 Cylinder         1024

 The values in the Sector Count Register and the SDH Register
 determine the sectors per track (SPT) and heads. Regardless of the
 values of the SPT and the heads, the drive is always in the
 translation mode.



**********************************************************************
                      G   E   N   E   R   A   L
**********************************************************************
WESTERN   TIPS

 WESTERN DIGITAL 3.5-INCH DRIVES FREQUENTLY ASKED QUESTIONS
 ----------------------------------------------------------
 1) Will a Caviar drive work in my system?
   If your computer is 100% AT compatible and has either a 40-pin AT
   IDE interface on the motherboard or an IDE controller card with a
   40-pin data cable.

 2) What are the master/slave jumper settings on Western Digital
    drives?
    All Western Digital drives are configured the same. On the back of
    the drive between the 4-pin power connector and the 40-pin data
    connector, there is a jumper block J8 consisting of 6 pins.
    Western Digital hard drives are shipped with a jumper shunt in the
    neutral storage position (across pins 5 and 3) for future dual
    drive use.

 - If you are installing the Western Digital hard drive as the only
   hard drive in your system, leave the jmper shunt in the neutral
   storage posiition. Jumper shunts are not required for single hard
   drive installations.

 - To designate the Western Digital hard drive as the master (C:),
   place a jumper shunt on pins 5-6

 - To designate the Western Digital hard drive as the slave (D:),
   place a jumper shunt on pins 3-4.

 3) What are the drive type and the drive parameters in the CMOS, for
    Western Digital drives?
    On top of the drive, the number of cylinders, heads and sectors
    per track are printed on the label. Precomp and L-zone should be
    set equal to the drive's cylinder count + 1. Select user type or
    custom type (typically type 41 or 42) for your drive. This will
    allow you to type in the parameters. Older systems that do not
    offer a user type can either upgrade the system BIOS or set the
    drive to drive type 1 (which should be a smaller drive size), and
    run Ontrack Disk Manager from A drive to get the full capacity of
    the drive. If you do not follow one of these procedures and your
    system is pre-1994, you will be limited to the largest size drive
    your BIOS will allow.

 4) What is the Ontrack Disk Manager software that came with my drive
    and what does it do?
    Ontrack Disk Manager is the original hard disk installation
    package that will initialize, partition, and prepare your hard
    drive for use. Ontrack Disk Manager also allows you to access the
    full capacity of the drive even when your system BIOS can't. It is
    compatible with 32-bit disk access.

 Note: Ontrack Disk Manager must be installed from floppy drive A. If
 your A drive is a 5.25-inch floppy drive, copy the contents of your
 Ontrack Disk Manager disk to a formatted 5.25-inch disk and re-run
 Ontrack Disk Manager.

 5) I just installed Ontrack Disk Manager on my Caviar drive and tried
    to install DOS. DOS attempted to write to my drive and it
    formatted my drive back to 528 MB which is my BIOS limitation. How
    do I install DOS and still get the full capacity of my drive?
    After Ontrack Disk Manager installation, you must create an
    Ontrack Disk Manager rescue disk. There are two ways of
    accomplishing this:

 OPTION 1:
 - Create a clean DOS bootable disk.

 - Copy 2 files from the Ontrack Disk Manager disk to your bootable
   disk: XBIOS.OVL, and DMDRVR.BINs Create a CONFIG.SYS file on this
   bootable disk with these 3 lines: DEVICE=DMDRVR.BIN FILES=35
   BUFFERS=35

 - Remove the floppy and reboot the system.

 - When you see the message "Press spacebar to boot from diskette",
   press the spacebar (system halts).

 - Insert the rescue disk in the A: drive.

 - Press any key (system resumes boot process).

 - At the A: prompt, remove rescue disk, insert DOS installation disk
   and type SETUP.

 - You can now install DOS without overwriting the Ontrack Disk
   Manager files.

 OPTION 2:

 - Create a clean DOS bootable disk.

 - Insert Ontrack Disk Manager disk in the A: drive.

 - At the A prompt, type: DMCFIG/D=A:. You will be prompted to insert
   a bootable floppy in the A: drive.

 - Follow the prompts on the screen. Ontrack Disk Manager will ask you
   to change disks a few times.

 - Continue until Ontrack Disk Manager is finished.

 - Remove the floppy and reboot the system.

 - When you see the message "Press spacebar to boot from diskette".
   Press the spacebar (system halts).

 - Insert the rescue disk in A drive.

 - Press any key (system resumes boot process).

 - At A prompt, remove rescue disk, insert DOS installation disk and
   type SETUP.

 - You can now install DOS without overwriting the Ontrack Disk
   Manager files.

 6) CHKDSK or SCANDISK reports a few bad sectors. How do I go about
    fixing the problem.
    You can use the Western Digital defect management utility WDATIDE.
    One of its options is the comprehensive surface analysis. This
    procedure will mark all grown defects bad if indeed there are any
    and it will compensate for the lost capacity by utilizing spare
    tracks.

 Note: This utility is data destructive. Back up all data on the drive
 before using it. Due to the thoroughness of this operation, WDATIDE
 can take quite a bit a time depending on the capacity of your drive.

 7) Do I have to do anything with my original drive when adding a new
    drive to my system?
    Yes, one hard drive must be designated as the master drive
    (preferably the newer, faster drive) and the other must be
    designated as the slave drive. Typically, most drives need to have
    a jumper placed on them to specify the Master or Slave position.
    For information on non-Caviar hard drives, please contact the
    appropriate manufacturer.

 8) I installed my new drive and entered the drive parameters in the
    CMOS, but the drive will not boot or it displays the message "HDD
    controller failure."
    Your drive must be partitioned and formatted before it will be
    bootable. If your system will support drives larger than 528 MB,
    and you have a copy of MS-DOS or PC-DOS version 5.0 or greater,
    insert the setup diskette in your floppy drive and turn on your
    computer. Follow the prompts and DOS will partition and format the
    drive for you.

 If you do not have a copy of MS-DOS or PC-DOS version 5.0 or greater,
 you will need to boot from a bootable disk and then run the FDISK
 command to partition your drive, and then format the drive using the
 DOS FORMAT command. After running format, you should be able to
 reboot your computer from your hard drive.

 9) How can I use the full capacity of my Caviar drive of 540 MB or
    greater?
    You can use Ontrack Disk Manager to obtain full capacity if your
    system does not support LBA mode. If your system does support LBA
    mode, you can enable LBA in your CMOS setup utility.

 10) How can I get 32-Bit Disk Access in Windows on my Caviar AC2540,
     AC2700 or AC31000 in Windows 3.1x? If your BIOS supports the
     drive at full capacity (i.e., the BIOS supports Logical Block
     Addressing) you use WDCDRV.386, Western Digital's FastDisk device
     driver. This driver is contained in a file named WIN31.EXE
     available for downloading from our bulletin board (714/753-1234),
     our Web server (WWW.WDC.COM), our FTP site (FTP.WDC.COM), our
     forum on the Microsoft Network (Go word WDC), and our forum on
     America On-line (keyword WDC). If your BIOS does not support LBA
     mode and you have installed your drive using Ontrack Disk Manager
     (v6.03 and above), run DMCFIG to install WDCDRV.386 and obtain
     32-Bit Disk Access.

 11) My drive will not spin up or spins down after a few seconds.
     This is a drive failure. Return the drive to the distributor or
     contact a technical support representative to receive a Return
     Materials Authorization (RMA).

 12) CMOS, FDISK and File Manager in Windows report less than the
     capacity of my new drive, but CHKDSK reports the right number of
     bytes. Which is correct?
     Setup (CMOS) and FDISK use a binary definition of a megabyte
     which is calculated at 1,048,256 bytes per megabyte. All hard
     drive manufacturers and the DOS CHKDSK utility use a decimal
     definition of a megabyte which is calculated at 1,000,000 bytes
     per megabyte. This is why some utilities show 515 MB for a 540
     megabyte drive and some show the actual number.

 13) How Can I install OS/2 for Windows, OS/2 3.0 WARP, Windows NT
     3.5x or Windows 95 on my drive which was initially installed
     using Ontrack Disk Manager?
     If you have Ontrack Disk Manager version 6.03, 6.03a, or 6.03b,
     download the file named DMPATCH.EXE from Western Digital's online
     services: ftp site: ftp.wdc.com

 World Wide Web Site: http://www.wdc.com/
 Microsoft Network (MSN) - Go word WDC
 America Online (AOL) - Keyword: Western Digital
 Western Digital's BBS at (714) 753-1234
 This file has the latest Ontrack Disk Manager drivers which will
 allow you to install OS/2 version 2.1x, OS/2 WARP, Windows NT 3.5x
 or Windows 95 on your hard drive. Please read the included readme
 file with this file for further detail.

 14) My drive will work as a slave but not as a master (or vice-
 versa).
 Check master/slave jumpers on all drives. Also, some drive's speed
 and timing differ drastically as to the initial spinup sequence. This
 might confuse the system and cause one of the drives not to be
 recognized. The best solution for this situation is to exchange
 drives (make the master a slave and vice-versa).

 15) My drive will not partition when I run FDISK. It hangs the system
     or it displays the message: "Runtime error."
     This is usually caused by corruption or damage to track zero. Use
     the Western Digital utility WDFMT to format the drive. If that
     does not help, call Western Digital Technical support at
     1-800-ASK-4-WDC to get further instructions.

 16) Can a hard drive be mounted on it's side, edge, or upside down?
     Drives can be mounted on any side but it is preferable to mount
     the drive right side up. It is also important to use all four
     screws to hold the drive firmly in place.


 Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T.)
 ----------------------------------------------------------------
 S.M.A.R.T. enables a drive's internal status to be monitored through
 diagnostic commands at the host level.

 The Caviar AC21600, AC32100 and AC32500 drives monitor read error
 rate, start/stop count, spin-up retry count, and drive calibration
 retry count. All of these attributes are updated and stored on the
 hard drive in the reserved area of the disk. The hard drive also
 stores a set of attribute thresholds that correspond to the
 calculated attribute values. Each attribute threshold indicates the
 point at which its corresponding attribute value achieves a negative
 reliability status.
 ====================================================================

  QUESTION
  Which hard drive specification is most important to overall
  system performance ?

 - Host Transfer Rate
 - Drive RPM (revolutions per minute)
 - Disk Transfer Rate (Media Rate)
 - Seek Time
 - Cache Size
 - PC Data Handling
 - All of the above

 Answer
 The correct answer is actually a combination of "all of the above,"
 keeping in mind most of the above specifications are interrelated
 when it comes to optimizing system performance.

 The pie chart illustrates the relative influence of factors affecting

 drive performance during a typical random I/O operation (reading
 and writing to a hard drive).

 The major determinate of hard drive performance is mechanical
 factors which are one hundred times slower than the high-speed
 electronics contained in a drive.


 Factors Affecting Hard Drive Performance
 (In their relative order of importance)

 MECHANICAL LATENCIES
 Mechanical Latencies include both Seek Time and Rotational
 Latency. The seek time is a measure (in milliseconds) of how
 fast the hard drive can move its read/write heads to a desired
 location. Rotational latency is a measure of the average time
 (also in milliseconds) the read/write heads must wait for the
 target sector on the disk to pass under them once the read/write
 heads are moved to the desired target track.

 Mechanical latencies are the main hindrance to higher performance
 in modern Enhanced IDE (EIDE) hard drives. The time delays of
 mechanical latencies are one hundred times higher than
 electronic (non-mechanical) latencies associated with the
 transferring of data. Therefore, reducing mechanical latencies
 (a lowering of seek time and rotational latency) should be the
 top consideration in improving hard drive performance.

 RPM
 This is the rotational speed of the media (disk), also referred
 to as the spindle speed. Hard drives only spin at one constant
 speed. Typical speeds are 3600 to 3880, 4500, and 5200 to 5400
 revolutions per minute. The slower the RPM, the higher the
 Mechanical Latencies. Disk RPM is a critical component of hard
 drive performance because it directly impacts the rotational latency
 and the Disk Transfer Rate explained below.

 DISK TRANSFER RATE
 The Disk Transfer Rate (sometimes called media rate) is the
 speed at which data is transferred to and from the disk media
 (actual disk platter) and is a function of the recording frequency.
 Typical units are bits per second (BPS), or bytes per second.
 Modern hard disks have an increasing range of Disk Transfer
 Rates from the inner diameter to the outer diameter of the disk.
 This is called a "zoned" recording technique.

 The key media recording parameters relating to density per platter
 are Tracks Per Inch (TPI) and Bits Per Inch (BPI). A track is a
 circular ring around the disk. TPI is the number of these tracks
 that can fit in a given area (inch). BPI defines how many bits
 can be written onto one inch of a track on a disk surface. To
 greatly simplify, the Disk Transfer Rate (the rate at which data
 is read and written to the disk) is dependent upon the speed of
 the disk (RPM) and the density of the data on the disk (BPI).
 Even most modern, high-speed, 5000 RPM hard drives are generally
 limited to a maximum Disk Transfer Rate of approximately 9 to 10
 MB per second. This specification is critical to performance and
 must be weighed carefully against such electronic latencies as
 Mode 3 PIO and Mode 4 PIO host transfer rates explained below.

 PC DATA HANDLING
 After the data moves down the IDE cable from the drive to the host
 interface, there are several factors that can affect drive
 performance over which the hard drive has no control. PC Data
 Handling is independent from the hard drive and very dependent
 upon the CPU type and speed, the BIOS overhead (how the system
 issues commands to the hard drive), speed and size of the system
 RAM and RAM cache, CPU-to-memory speed, and storage subsystem
 performance. PC Data Handling is also affected by the caching
 methods of such software applications as SMARTDRIVE, 32-bit
 disk access operating system drivers, etc.

 HOST TRANSFER RATE
 The speed at which the host computer can transfer data across the
 IDE or EIDE interface. Processor Input/Output (PIO) modes and
 Direct Memory Access (DMA) modes are defined in the ATA-2 industry
 specification as follows:

 Mode 3 PIO  11.1 MB/sec
 Mode 4 PIO  16.6 MB/sec
 Mode 1 DMA  13.3 MB/sec
 Mode 2 DMA  16.6 MB/sec

 Modern host computer systems usually support most of the above
 modes. Faster Host Transfer Rates in the future will use multi-word
 DMA modes as the industry will not support any future PIO mode
 standards beyond mode 4.

 The computer system manufacturer is responsible for implementing a
 Host Transfer Rate that is high enough to ensure that the host
 computer is not the performance bottleneck. Implementing
 increasingly higher Host Transfer Rates without corresponding
 increases in Disk Transfer Rates on the hard drive will not result
 in increased drive performance.


 Cache Buffer Size - Is Bigger Always Better ?
 A Cache Buffer is similar to a water glass. When you are writing
 to a hard drive, the host computer fills the glass and the disk
 media empties it. If you are reading data from a hard drive, the
 disk media fills the glass and the host computer empties it.

 The reason that a bigger cache buffer is not always better
 (or faster) is because the host computer (with Mode 4 PIO or
 Mode 2 DMA capabilities) can empty or fill the glass much faster
 than the hard drive can empty or fill it. When the host system can
 transfer data in or out of the cache buffer faster than the media
 rate, a larger buffer size becomes irrelevant because the host
 system is always "waiting" for the hard drive.

 Western Digital hard drives are designed with cache buffer sizes
 that are matched to the Disk Transfer Rate capabilities of the
 drive and the Host Transfer Rates of modern computer systems. All
 of our drives are benchmarked with various cache buffer sizes to
 verify that the most cost-effective and performance-effective
 cache size is implemented.


 Confusion Over Mode 4 and Mode 2 DMA
 The Enhanced IDE program created the long-range road map for
 performance enhancements which included faster disk and host
 transfers, Mode 3, Mode 4, Mode 2 DMA, etc. Currently, computer
 systems and hard drive controller silicon have most of the elements
 needed to implement Mode 4 PIO or Mode 2 DMA (a 16.6 MB/sec Host
 Transfer Rate). However, to take advantage of these performance
 modes, physical drive architecture must also make some performance
 improvements in the area of Mechanical Latencies and Disk Transfer
 Rate (media rate) as defined earlier.

 Some competitors, in their eagerness to supply a new feature, are
 prematurely marketing Mode 4 and Mode 2 DMA. While their drive
 controller silicon supports these modes (which is very easy and
 inexpensive to implement), spindle speeds (RPM), rotational latency,
 bit density, and other factors have not yet been improved (these
 being very difficult and costly). The result is hard drives which
 have the electronic capability to do Mode 4 and Mode 2 DMA transfer
 rates, but can't take advantage of these modes due to the slower
 Disk Transfer Rate of the drive.

 Western Digital will not be implementing Mode 4 or Mode 2 DMA on
 older drive products as the host systems into which these drives
 are designed are not electrically capable of these data transfers,
 nor are the Disk Transfer Rates on these drives beyond current Mode
 3 capabilities. As next generation systems are introduced, they will
 be paired with next generation drives. Those drives will require
 and offer true Mode 4 / Mode 2 DMA capability from a total drive
 architecture standpoint.
 =====================================================================
 AC2540/2635/2700/2850/21000/31000/31200/31600

 Windows 95 Operating System Addendum
 ------------------------------------
 The information in this addendum supersedes that supplied in Windows
 95 section on pages 35 and 36 of this manual. Please refer to thos
 addendum for Windows 95 questions.

 Although Windows 95 is capable of recognizing the full capacity of
 hard drives larger than 528 MB in systems with a translating BIOS,
 some restrictions apply to systems without a translating BIOS.


 For Systems With a Translating BIOS
 -----------------------------------
 Enter your CMOS setup and select a drive type that will recognize the
 full capacity of your drive. This is usually done by selecting the
 auto config drive tape. The boot partition can be set up to be as
 large as the full capacity of your hard drive.


 For Systems Without a Translating BIOS
 --------------------------------------
 Enter your CMOS setup and select a user defined drive type. Enter
 these parameters: cylinders = 1024, heads = 16, sectors = 63. Your
 system's total disk space will be limited to a maximum of 528MB.

 If you want your system to utilize more than 528 MB of disk space,
 you must use Ontrack's Disk Manager software (or a similar third-
 party installation software).


 Installing Windows 95 on a Hard Drive with Ontrack Disk Manager
 Already Installed
 ---------------------------------------------------------------
 The Windows 95 installation program will analyze your computer
 system and install seamlessly with Ontrack Disk Manager.


 Computer Systems with Windows 95 Already Installed
 --------------------------------------------------
 If you are installing a Western Digital hard drive and Ontrack Disk
 Manager on a computer system with Windows 95 already installed, you
 must install Ontrack Disk Manager as described here.

 Enter your CMOS setup and select a user defined drive type. Enter
 these parameters for drives with capacities over 528MB:
         Cylinders = 1024, Heads = 16, Sectors = 63.

 Save these changes and reboot your computer.

 1. Select the Start icon from the Windows 95 main screen.
    DO NOT open an MS-DOS menu from Win 95 to install Ontrack Disk
    Manager.

 2. Choose the Shut Down option.

 3. Select Resatrt Computer in DOS mode. When your computer restarts,
    you should be at the DOS prompt.

 4. Install Ontrack Disk Manager.

 Windows 95 will noe recognize the full capacity of your hard drive
 and run in 32-bit disk access mode for optimum performance.


