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+                ATA/ATA-1/ATA-2/IDE/EIDE/etc FAQ
+
+                    Part 1 of ? -- The Basics
+
+                      Version 0b -- 7 Feb 95
+
+             by Hale Landis -- landis@sugs.tware.com
+
+Note:  Major changes from the previous version are marked by a
+   "!" at the left margin on the first line of the changed
+   paragraph.
+
+First the "legal" stuff...
+
+   1) This FAQ is not intended to replace any other FAQ on this
+   subject but is an attempt to provide historical and technical
+   information about the ATA interface.
+
+   2) This FAQ is not an endorsement of any vendor's product(s).
+
+   3) This FAQ is not a recommendation to purchase any vendor's
+   product(s).
+
+   4) Every effort is made to insure that all of the information
+   presented here is not copyrighted, not proprietary and
+   unrestricted.
+
+   4) When opinions are stated they are clearly identified,
+   including the person's name and email address.  Such opinions
+   are offered as long as they contribute to the understanding of
+   the subject being discussed.  No "flames" allowed.
+
+This is the first version of this FAQ.  It will take some time to
+get all the significant information into it so it will be rapidly
+growing and changing during the next several weeks or months.  I
+don't even know how many parts there will be yet!  Versions will
+be numbered with simple integer numbers (no 1.1, 1.2, etc)
+starting at 0.
+
+If you have a question that is not answered here or if you have
+unrestricted material that you would like to contribute, please
+email it to landis@sugs.tware.com.  DO NOT send material that is
+copyrighted, proprietary or otherwise restricted in any way -- I
+can't use such material in this document.
+
+I don't have FTP access to anything at this time so I leave it to
+others to put this at the appropriate FAQ FTP sites.
+
+About myself:  Until recently I worked for Seagate where I was
+one of several people that attended the ATA, ATA-2, PCMCIA and
+SFF meetings for Seagate.  I was also the manager of a software
+development group that created much of the engineering test
+software for ATA hard disk drives.  I am now a consultant and I
+still attend the ATA-2 meetings.
+
+Table of Contents
+-----------------
+
+Part 1 - The Basics
+
+   Glossary
+   Basic Questions
+
+Part 2 - BIOS and Drivers
+
+   TBD
+
+
+Glossary
+--------
+
+Read and understand these terms.  You will be lost and confused
+if you don't!  Many of these are describe in much greater detail
+in other parts of this FAQ.
+
+ATA or AT Attachment
+
+   ATA is the proper and correct name for what most people call
+   IDE.  In this document, ATA refers to all forms of ATA (ATA-1,
+   ATA-2, etc, IDE, EIDE, etc).  The ATA interface uses a single
+   40-conductor cable in most desktop systems.
+
+ATA-1
+
+   ATA-1 is the common name of the original ATA (IDE)
+   specification.  ATA-1 is not an official standard yet.  Final
+   approval is pending.
+
+ATA-2 or ATA Extensions
+
+   ATA-2 is the common name of the new ATA specification.  ATA-2
+   is still in early draft form and has not been submitted for
+   approval as an official standard.
+
+ATA-3
+
+!  ATA-3 is the common name of a future version of the ATA
+   specification.  The ATA-3 working group has held several
+   meeting but the only things adopted so far are a DMA
+   version of the Identify command, a description of
+   "device 1 only configurations" and a set of "security"
+   commands.
+
+!  There is much discussion going on concerning merging ATA-3
+   with ATAPI.  This will require some kind of "command overlap"
+   capability.  The details of this are consumming much of the
+   meeting time.
+
+ATAPI or ATA Packet Interface
+
+   ATAPI is a proposed new interface specification.  Initially it
+   will probably be used for CD-ROM and tape devices.  It uses
+   the ATA hardware interface at the physical level but uses a
+   subset of the SCSI command set at the logical level.  The
+   ATAPI specification work is currently being done in the SFF
+   committee.
+
+!  The ATAPI folks have delayed forwarding their CD-ROM
+   specification from SFF to X3T10 so the X3T10 ATAPI working
+   group has nothing to work on yet and have held no meetings.
+
+! Block Mode
+
+!  Block mode is the name given to the use of the ATA Read
+   Multiple and Write Multiple commands.  These commands generate
+   a single interrupt to the host system for each block of
+   sectors transfered.  The traditional Read Sectors and Write
+   Sectors commands generate an interrupt to the host for each
+   sector transfered.
+
+CAM (Common Access Method) Committee
+
+   The Common Access Method committee, now disbanded, worked on
+   two specifications: the CAM SCSI and CAM ATA specifications.
+   Both specifications were forwarded to the X3T9 committee for
+   further work years ago.
+
+CHS or Cylinder/Head/Sector
+
+   CHS is the old and traditional way to address data sectors on
+   a hard disk.  This style of addressing relates a sector's
+   address to the position of the read/write heads.  In today's
+   ATA devices, all sector addresses used by the host are logical
+   and have nothing to do with the actual physical position of
+   the sector on the media or the actual position of the
+   read/write heads.
+
+Command Block
+Control Block
+
+   These are names given to the I/O register interface used by
+   ATA devices.  It refers to a set of I/O registers, or I/O
+   ports and I/O port addresses used to program the device.
+   These names replace the older term Task File.
+
+DMA or Direct Memory Access
+
+   DMA is a method of data transfer between two devices that does
+   not use the system's main processor as part of the data path.
+   DMA requires lots of hardware:  a DMA arbitration unit, a DMA
+   data transfer unit and host bus signals that enable the DMA
+   controller to assume control of the host system's bus.  When
+   the DMA controller has control of the host system's bus, it
+   moves data between the two devices by generating the
+   appropriate bus read/write cycles.  For the ATA READ DMA
+   command this means generating an I/O read cycle and then a
+   memory write cycle for each 16-bit word being transferred.
+   For the ATA WRITE DMA command, a memory read cycle is followed
+   by an I/O write cycle for each 16-bit word transferred.
+
+EIDE or Enhanced IDE
+
+   EIDE is a marketing program started by Western Digital to
+   promote certain ATA-2 features including ATAPI.  WD has
+   encouraged other product vendors to mark their products as
+   "EIDE compatible" or "EIDE capable".
+
+ESDI
+
+   See MFM.
+
+Fast ATA
+
+   Fast ATA is a Seagate marketing program used to promote
+   certain ATA-2 features in newer ATA devices.  Seagate has
+   encouraged other product vendors to mark their products as
+   "Fast ATA compatible" or "Fast ATA capable".
+
+Host or Host System
+
+   The computer system that the ATA device is attached to.
+
+HBA or Host Bus Adapter or Host Adapter
+
+   The hardware that converts host bus signals to/from ATA
+   interface signals.  An ATA-1 host adapter is generally a very
+   simple piece of hardware.  An ATA-2 host adapter can be simple
+   or complex.
+
+IDE
+
+   IDE can mean any number of things:  Imbedded Device (or Drive)
+   Electronics (yes, you can spell embedded with an "i"),
+   Intelligent Device (or Drive) Electronics, etc.  The term IDE
+   is the trademark of someone (Western Digital does not claim
+   IDE as theirs but they do claim EIDE).  Many hard disk vendors
+   do not use IDE to describe their products to avoid any
+   trademark conflicts.
+
+LBA or Logical Block Addressing
+
+   LBA is a newer (for ATA it is newer) way to address data
+   sectors on a hard disc.  This style of addressing uses a
+   28-bit binary number to address a sector.  LBA numbers start
+   at zero.  In today's ATA devices, all sector addresses used by
+   the host are logical and have nothing to do with the actual
+   physical location of the sector on the media.
+
+Local Bus
+
+   Usually this refers to the processor's local bus in a high
+   performance computer system.  Usually the processor, the
+   external processor instruction/data cache, the main memory
+   controller and the bridge controller for the next low speed
+   system bus, for example, a PCI bus, are located on the local
+   bus.  Lower speed local buses may have connectors that allow
+   the attachment of other devices.  For example, the VL-Bus is a
+   local bus that can allow attachment of video, SCSI or ATA
+   controllers.  It is very difficult to attach other devices to
+   high speed (say faster than 100MHz) local buses due to
+   electrical restrictions that come into play at those higher
+   speeds.
+
+Master
+
+   ATA device 0.  Device 0, the master, is the "master" of
+   nothing.  See Slave.
+
+Megabyte or MB
+
+   Megabyte or MB is 1,000,000 bytes or 10^6 bytes.  IT IS NOT
+   1,048,576 bytes or 2^20 bytes, repeat NOT!
+
+MFM
+
+   In this document MFM refers to any of the older hard disk
+   controller interfaces, MFM, RLL and ESDI.  It is used to
+   describe any hard disk controller that uses the Task File
+   interface on the host side and the ST506/ST412 interface
+   on the drive side.
+
+OS
+
+   Operating System.
+
+PC Card ATA
+PCMCIA
+
+   We can thank the Personal Computer Memory Card International
+   Association for the PC Card specification.  The PCMCIA is a
+   nonprofit industry association.  The PC Card ATA
+   specification is another form of the ATA interface used by
+   PCMCIA compatible ATA devices.  This interface uses the PCMCIA
+   68-pin connector.  Most 68-pin ATA devices are dual mode --
+   they can operate as either a PCMCIA PC Card ATA device or as a
+   68-pin ATA device.
+
+PCI
+
+   We can thank Intel and the other members of the PCI committee
+   for the PCI bus specification.  PCI is intended to be the next
+   high performance computer bus.  PCI is not generally described
+   as a processor local bus.
+
+PIO or Programmed Input/Output
+
+   PIO is a method of data transfer between two devices that uses
+   the system's main processor as part of the data path.  On
+   x86 systems, the REP INS and REP OUT instructions
+   implement this data transfer method.  INS reads and I/O port
+   and writes the data into memory.  OUTS reads data from memory
+   and writes the data to an I/O port.  Each time an INS or OUTS
+   instruction is executed, the memory address is updated.  The
+   REP prefix causes the instructions to be repeated until a
+   counter reaches zero.
+
+RLL
+
+   See MFM.
+
+Slave
+
+   ATA device 1.  Device 1, the slave, is a "slave" to nothing.
+   See Master.
+
+Task File
+
+   This is the name given to the I/O register interface used by
+   MFM controllers.  It refers to a set of I/O registers, or I/O
+   ports and I/O port addresses used to program the controller.
+   In ATA, this name has been replaced by the terms Command Block
+   and Control Block.
+
+SCSI
+
+   See the SCSI FAQ.
+
+SFF or Small Form Factor
+
+   The SFF committee is an ad hoc committee formed by most of the
+   major storage device and system vendors to set standards for
+   the physical layout of hard disk and other devices.  SFF has
+   published many specifications that describe the physical
+   mounting and connector specifications for hard disk devices,
+   including ATA devices.  During a brief period of time when the
+   X3T9 committee was not doing much work on the ATA-1 interface,
+   the SFF committee published several specifications that were
+   not really part of the original SFF charter.  Most, if not
+   all, of these nonphysical specifications have now been
+   incorporated into the latest X3T9 or X3T10 ATA specifications.
+   ATAPI is currently an SFF specification.
+
+ST506 and ST412
+
+   This is the common name for the hard disk controller to hard
+   disk drive interface used by MFM, RLL and ESDI controllers and
+   disk drives.  ST stands for Seagate Technology.  The ST506 and
+   ST412 were the Seagate products that set the de facto
+   standards for this interface many years ago.  This interface
+   is composed of two cables:  a 34-conductor and a 20-conductor
+   cable.
+
+VESA and VL-Bus
+
+   We can thank the Video Electronics Standards Association for
+   the VESA Local Bus or VL-Bus specification.  The VL-Bus is one
+   example of a local bus.  VESA is a nonprofit industry
+   association like the PCMCIA.
+
+WG or Working Group
+
+   The actual work on various specifications and standards
+   documents within the X3T9, X3T10 and SFF committees happens in
+   working group meetings.  Most WG meetings are held monthly.
+
+X3T9 and X3T10
+
+   These are the names of the official standards committees that
+   have worked on the ATA-1 and ATA-2 specifications.  X3T9 was
+   responsible for the SCSI and ATA-1 specifications and
+   standards.  X3T10 has replaced X3T9 and is now responsible for
+   the current SCSI and ATA specifications and standards work.
+
+528MB
+
+   This term is used in this document to describe the capacity
+   boundary that exists in most x86 system software.  This
+   boundary limits the size of an ATA disk drive to 528MB.  For
+   cylinder/head/sector style addressing of disk data sectors,
+   this number is computed as follows:
+
+   a) the number of cylinders are limited to 1024, numbered
+   0-1023.
+
+   b) the number of heads (per cylinder) are limited to 16,
+   numbered 0-15,
+
+   c) the number of sectors (per track) are limited to 63,
+   numbered 1-63.
+
+   d) a sector is 512 bytes,
+
+   e) 528MB means the following values:
+
+      ( 1024 * 16 * 63 ) or 1,032,192 data sectors
+
+      or
+
+      ( 1024 * 16 * 63 * 512 ) or 528,482,304 bytes.
+
+68-pin ATA
+
+   This refers to a variation of the ATA interface that uses the
+   PCMCIA 68-pin physical interface but does not use the PCMCIA
+   electrical or logical interface.  Most 68-pin ATA devices are
+   dual mode -- they can operate as either a PCMCIA PC Card ATA
+   device or as a 68-pin ATA device.  This interface was
+   developed within the SFF committee and is now included in
+   ATA-2.
+
+Basic Questions
+---------------
+
+### Where did ATA come from?
+
+   What we now call the ATA-1 interface was developed for Compaq
+   many years ago by Imprimus (then part of CDC, now part of
+   Seagate) and Western Digital.  The first ATA-1 hard disk
+   drives were made by Imprimus but it was Conner that made the
+   interface so popular.
+
+### How is ATA different from MFM?
+
+   From the host software standpoint, ATA is very much like the
+   Task File interface used by MFM controllers.  A properly
+   written host software driver should not notice any difference
+   between the MFM Task File interface and the ATA Command Block
+   interface while doing basic commands such as Read/Write
+   Sectors.
+
+   At the hardware level, ATA uses a single cable between a host
+   bus adapter and the ATA device, where the MFM controller
+   interface uses two cables between the controller and the
+   drive.
+
+   In the MFM environment, the controller is one piece of
+   hardware and the drive another piece of hardware.  Most likely
+   these two pieces of hardware are from different vendors.  The
+   MFM controller is dependent on the design of both the host bus
+   and on the drive.
+
+   In the ATA environment, the host adapter is the one piece of
+   hardware that is dependent on the host system bus design.  The
+   ATA interface is (mostly) system independent.  All of the
+   hard disk controller and drive logic is contained in the ATA
+   device hardware.  This gives the hard disk designer complete
+   control over both the controller and drive functions.
+
+### Why is ATA so popular?
+
+   Two basic things make ATA so popular today:  cost and hard
+   disk drive technology.  An ATA-1 host adapter is cheap,
+   usually much less than $25US and it uses only one cable.  On
+   the technology side, current hard disk features, such as,
+   defect handling, error recovery, zone recording, cache
+   management and power management require that the controller be
+   fully integrated with the read/write channel, the servo system
+   and spindle hardware of the disk drive.
+
+### What are the basics of the ATA interface?
+
+   The ATA interface is a very simple interface based on an ISA
+   bus I/O device architecture.  The interface consists of two
+   sets of I/O registers, mostly 8-bit, for passing command and
+   status information.  The registers are like a set of mail
+   boxes with a door on front and back connected such that both
+   doors can not be open at the same time.  The front door is
+   open when the Busy bit in the Status register is zero and the
+   host can read and write the registers.  The back door is open
+   when the Busy bit in the Status register is one and the ATA
+   device can read or write the registers.
+
+   The physical interface contains just enough signals for a 16
+   bit data bus, five register address bits, and a few control
+   signals like read register, write register and reset.
+
+   ATA devices look like traditional hard disk
+   drives even though some are not really a hard disc with
+   rotating platters.  User data is recorded in 512 byte sectors.
+   Each sector has a sector address.  There are two ways to
+   express sector addresses:  by cylinder/head/sector (CHS) or by
+   logical block address (LBA).  CHS is standard, LBA is optional.
+
+### What is EIDE or Fast ATA?
+
+   Both are marketing programs used to promote various ATA-2
+   features, mostly the faster data transfer rates defined by
+   ATA-2.
+
+   ---
+
+   WD defines EIDE as:
+
+   * Support for drives larger than 528MB.
+
+   * Support for two connectors to allow up to four drives.
+
+   * Support for CD-ROM and tape peripherals.
+
+   * Support for 11.1/16.6 Mbytes/second, I/O Channel Ready PIO
+     data transfers.
+
+   * Support for 13.3/16.6 Mbytes/second, DMA data transfers.
+
+   ---
+
+???Seagate defines Fast ATA as:
+
+   * Support for PIO mode 3 (11.1 MB/sec) and DMA mode 1(13.3
+     MB/sec).
+
+   * Support for Multi-sector [Read/Write Multiple] transfers.
+
+   * Support for >528 MB.
+
+   * Support for Identify Drive Extensions & Set Transfer Mode
+     Extensions.
+
+   * Backward compatibility with ATA-1.
+
+   ---
+
+   What does all of this mean to us?
+
+   Support for the ATA-2 high speed PIO and DMA data transfer
+   modes is both a hardware and software issue.
+
+   Support for more than one hard disc controller (or ATA host
+   adapter) requires the BIOS and/or the operating system to
+   support more than one Task File or Command/Control Block
+   register set on the host bus.
+
+   The 528MB problem is due to the original design of the x86
+   BIOS which limits cylinders to 1024 and sectors to 63.  The
+   ATA interface allows up to 65,535 cylinders, 16 heads and 255
+   sectors -- that's about 136GB (137GB if is LBA is used).
+   Support for devices over 528MB requires the BIOS and/or
+   operating system to support some form of CHS translation.
+   Note that LBA alone does not solve this problem (in fact,
+   LBA may make things more complex).
+
+   Support for CD-ROM and tape will probably be done via the
+   ATAPI interface which uses a different command structure than
+   ATA.  That makes ATAPI another host software issue.
+
+### What does an ATA-1 host adapter do?
+
+   An ATA-1 host adapter is a simple piece of logic whose main
+   purpose is to reduce the system bus address lines from 12 (or
+   more) down to 5. It may also buffer some signals giving some
+   degree of electrical isolation between the host bus (usually
+   an ISA or EISA bus) and the ATA bus.  In ATA-1, the ATA
+   interface is controlled directly by the host bus so that all
+   timings are controlled by the host bus timing.
+
+### What does an ATA-2 host adapter do?
+
+   This answer is complex because it depends on how smart your
+   ATA-2 host adapter is.  First, an ATA-2 host adapter supports
+   the ATA-2 higher speed data transfer rates.  That requires
+   that the host adapter is attached to something other than an
+   ISA or EISA bus.  Second, an ATA-2 host adapter may perform
+   32-bit wide transfers on the host bus.  This requires FIFO
+   logic and data buffers in the host adapter.  Third, an ATA-2
+   host adapter may use a different data transfer protocol on the
+   host side than is used on the ATA device side.
+
+! ### Can I put an ATA-2 device on an ATA-1 host adapter?
+! ### Can I put an ATA-1 device on an ATA-2 host adapter?
+
+   The answer to both questions is yes, as long as the electrical
+   timing specifications of the device are not violated.  In
+   general it is impossible for an ATA-1 host adapter to violate
+   the specifications of an ATA-2 device.  It is possible for an
+   ATA-2 host adapter to violate the timing specifications of an
+   ATA-1 device but this is not common.  Hoever, host adapter
+   hardware design errors or software driver bugs can cause such
+   a problem.  The result will be corrupted data read or written
+   to the ATA-1 device.
+
+! ### I have an ATA-2 host adapter with an ATA-2 device.  I want to
+! ### add an ATA-1 device to this host adapter.  Can I run the ATA-2
+! ### device in its ATA-2 data transfer modes?
+
+   Sorry, *NO* you can *NOT* run the new drive in its faster data
+   transfer modes.  Be very careful, most of the ATA-2 host
+   adapter vendors don't have anything in their setup
+   documentation or software to prevent this sort of thing.
+
+   When you run the new drive at a data transfer speed that is
+   faster than the older drive can support, you are violating the
+   electrical interface setup and hold times on the older drive.
+   There is no telling what the older drive will do about this,
+   but you are asking for data corruption and other nasty
+   problems on your older drive.
+
+### How many disk controllers and/or ATA host adapters and/or
+### SCSI host adapters can I put in my system?
+
+   From a hardware standpoint -- as many as you want as long as
+   there are no I/O port address, memory address or interrupt
+   request signal conflicts.  From a software standpoint it is a
+   whole different story.
+
+   First the simple x86 system hard disk controller
+   configurations...
+
+   a) 1 ATA with 1 or 2 drives at I/O port addresses
+   1Fxh/3Fxh using interrupt request 14 (IRQ14).
+
+   b) 1 ATA with 1 drive at I/O port addresses 1Fxh/3Fxh
+   using interrupt request 14 (IRQ14) plus a SCSI with 1 drive.
+
+   c) 1 SCSI with 1 or 2 drives.
+
+   Other configurations are possible but are most likely not
+   supported in the system or SCSI host adapter BIOS.  And if its
+   not supported at the BIOS level, it is unlikely to be
+   supported by an operating system, especially DOS.  The primary
+   reason the above configurations are so restrictive is that the
+   original IBM x86 BIOS supported only one MFM controller with a
+   maximum of 2 drives.  This restriction was then coded into
+   much x86 software including many early version of DOS.  The
+   configurations above work because they don't break this old
+   rule.
+
+   Just remember this -- most systems will always boot from
+   the first drive on the first controller.  In a) that is
+   ATA drive 0, in b) that is ATA drive 0, in c) that is
+   SCSI drive 0.
+
+   And now the more complex configurations...
+
+   Once you go beyond the three configurations above all bets are
+   off.  Most likely you will need operating system device
+   drivers in order to access any drives beyond the first two.
+   And now your real problems start especially if you like to run
+   more than one operating system!
+
+   If you do run more than one OS, then you need equivalent
+   drivers for each system if you would like to access all the
+   drives.  Plus it would be nice if all the drivers configured
+   the drives in the same manner and supported all the possible
+   partitioning schemes and partition sizes.  It would be
+   especially nice if a driver would not destroy the data in a
+   partition just because it did not understand the file system
+   format in that partition.
+
+   One of the things EIDE promotes is BIOS support for up to four
+   ATA devices -- 2 ATA host adapters each with 1 or 2 drives.
+   The first would be at I/O port addresses 1Fxh/3Fxh using
+   interrupt request 14 (IRQ14) and the second at I/O port
+   addresses 17xh/37xh using interrupt request 15 (IRQ15).
+   Acceptance of this configuration has not been spreading like
+   wild fire through the BIOS world.
+
+   Lets look at a two complex configurations...
+
+   a) 1 ATA with 2 drives and 1 SCSI with 1 or more drives.
+
+   Nice configuration.  The ATA drives would be supported by the
+   system BIOS and the SCSI drives may be, could be, should be,
+   supported by the SCSI host adapter BIOS but probably not.  So
+   in order to use the 2 SCSI drives you probably have to disable
+   the BIOS on the SCSI card and then load a device driver in
+   CONFIG.SYS.  And because the SCSI BIOS is disabled, you then
+   need a SCSI driver for that other OS you run.
+
+   b) 2 ATA with 1 or 2 drives on each.
+
+   Also a nice configuration.  But because the system BIOS
+   probably only supports the first controller address, you'll
+   need a DOS device driver loaded in CONFIG.SYS in order to
+   access the drives on the second controller.  You'll need that
+   driver even if there is only one drive on the first
+   controller.  You also need a similar driver to support the
+   second controller in your other OS.
+
+   Note:  I understand that OS/2 does support both MFM/ATA
+   controller addresses and does allow up to four drives -- I
+   have not confirmed this for myself.
+
+! ### Are disk drives the only ATA devices?
+
+   No.  Over the years there have been ATA tape drives, ATA
+   CD-ROMS and other strange devices.  Most of these are expected
+   to be added to an existing ATA host adapter as the second
+   device (device 1) with an existing ATA disk drive (device 0).
+   In general these require software drivers to operate with your
+   OS.
+
+   Now, we have ATAPI CD-ROM and tape devices that can be placed
+   on an ATA host adapter.  And soon we should see system
+   motherboard BIOS support for booting from an ATAPI CD-ROM
+   device.  The general idea is that an ATAPI device can coexist
+   with an ATA device on the same cable.
+
+! ### What can be done to improve ATA device performance?
+
+   A difficult question.  But the first step is usually to reduce
+   the number of interrupts that the host sees during a read or
+   write command.  ATA disk drives have three types of read/write
+   commands:
+
+   * Read Sectors / Write Sectors -- These commands are the old
+   traditional data transfer commands.  These commands generate
+   one interrupt to the host for each sector transfered.  These
+   are PIO data in and PIO data out commands which use the host
+   processor to transfer the data.
+
+   * Read Multiple / Write Multiple -- These commands where
+   defined in ATA-1 but were not used very much until recently.
+   These commands generate one interrupt to the host for each
+   block of sectors transfered.  The number of sector per block
+   is generally 4, 8 or 16.  However, when 1 sector per block is
+   used, these commands are the same as the Read/Write Sectors
+   commands.  These are PIO data in and PIO data out commands
+   which use the host processor to transfer the data.
+
+   * Read DMA / Write DMA -- These commands where defined in
+   ATA-1 but were not used very much until recently.  The main
+   reason for not using them was that x86 system DMA transfer
+   rates are much slower than PIO.  However, these command do
+   generate a single interrupt at the completion of the command.
+
+   Now see the next question...
+
+! ### What else can be done to improve ATA device performance?
+! ### -or-
+! ### What is PIO mode "x" ?
+
+   An even more difficult question.  The second step is usually
+   to increase the rate at which the host transfers data.
+
+   (Ahh...  I can see the funny look on your face from here.  You
+   are saying to yourself:  "the rate at which the host transfers
+   data? doesn't this guy have things backwards?"  Read on...)
+
+   The rate at which data is transferred to or from an ATA device
+   is determined by only one thing:  the PIO or DMA cycle time
+   the host uses.  No, the drive does not have much to do with
+   this!  The only requirement is that the host not exceed the
+   minimum PIO or DMA cycle times that the device supports.  For
+   example, during a PIO read command when the device signals an
+   interrupt to the host this means that the device is waiting
+   for the host to read the next sector or block of sectors from
+   the drive.  The host must execute a REP INSW instruction to do
+   transfer the data.  The rate at which the host executes this
+   instruction determines the PIO cycle time.  Technically, for a
+   read command, the cycle time is the time from the host
+   assertion of the I/O Read signal to the next time the host
+   asserts the I/O Read signal.
+
+   Be careful when looking at the table below -- the data rate is
+   the data transfer rate achieved while transfering the sector
+   or block or sectors.  It is an "instantanous" data rate.  The
+   overall data transfer rate for a command includes many time
+   consuming events such as the amount of time the host requires
+   to process an interrupt.  Note that on many fast ATA drives
+   today, the time it takes the host to process an interrupt is
+   frequently greater than the time required to transfer the
+   sector of block of sectors for that interrupt!  It is not
+   uncommon for the host overhead to reduce the data rate to 1/2
+   or 1/3 of the instantanous rate shown here.
+
+   The ATA PIO modes are defined as follows:
+
+   PIO   min cycle  data  comment
+   mode    time     rate
+
+    0      ???ns     ?MB  the rate at which a system
+                          running at 4.77MHZ could
+                          execute the REP INSW.
+
+    1      ???ns     ?MB  the rate at which a system
+                          running at 6MHz could
+                          execute the REP INSW.
+
+    2      240ns     8MB  the rate at which a system
+                          running at 8MHz could
+                          execute the REP INSW.
+
+    3      180ns    13MB  requires an ATA-2
+                          host adapter.
+
+    4      120ns    16MB  requires an ATA-2
+                          host adapter.
+
+   The complete description of the PIO (and DMA modes is much
+   more complex and will be cover in more detail later in this
+   FAQ.
+
+### Do I need BIOS or OS drivers to support more than 528MB?
+
+   Warning:  Read the previous question before reading this one.
+
+   Maybe, probably, yes.  The answer to this *very* complex and
+   will be discussed in detail in Part 2. Here is the brief
+   answer...
+
+   A traditional x86 system BIOS supports only CHS mode
+   addressing with cylinders limited to 1024, heads limited to 16
+   and sectors limited to 63.  This allows addressing of drives
+   up to 528MB.  These limitations come from the INT 13
+   read/write calls that combine a 10-bit cylinder number with a
+   6-bit sector number into a 16-bit register.
+
+   Note that this is entirely a software problem:  the ATA
+   interface supports up to 65,535 cylinders, 16 heads and 255
+   sectors.
+
+   While the head number usually requires only 4-bits, up to 6 or
+   8 bits are available in the INT 13 interface.  This fact has
+   allowed the SCSI folks to support big drives by increasing the
+   number of heads above 16.  The SCSI host adapter BIOS converts
+   this "fake" CHS address to a different CHS or an LBA when it
+   issues a read/write command to the drive.  The following table
+   shows some approximate drives sizes and the "fake" CHS
+   parameters that you may see from a SCSI BIOS:
+
+      cyl    head    sector   size
+
+      1024     16        63   512MB
+      1024     32        63     1GB
+       512     64        63     1GB
+      1024     64        63     2GB
+      1024    256        63     8GB
+
+   The last entry represents the largest possible drive that
+   a traditional INT 13 BIOS can support.
+
+   The system BIOS folks *must* start supporting drives over
+   528MB in their BIOS by implementing some type of CHS
+   translation.  To date, few systems have such BIOS.  And here
+   is the bad part:  Microsoft says that the BIOS *must*
+   support it in order to use it in their OS.  The algorithm is
+   simple (but warning:  this is not the complete algorithm!):
+
+      INT 13 input    action            ATA interface
+
+      cyl number      "multiply" by n   modified cyl number
+      head number     "divide" by n     modified head number
+      sector number   nothing           sector number
+
+   The value of n must be selected such that the modified head
+   number is less than 16.
+
+   LBA addressing at the hard disk drive level or at the BIOS or
+   driver level is another solution.  This solution will probably
+   not be popular for several more years.  It requires that the
+   BIOS people implement a new INT 13 interface, called the
+   Microsoft/IBM Extensions and that the OS people start using
+   this new BIOS interface.  Few system BIOS support this
+   alternative interface today.  Without this new interface, LBA
+   support at the hard disk drive level is not required.
+
+   So most of us have older systems without much possibility of
+   getting a BIOS upgrade, so what do we do?  Well we must obtain
+   one of the many driver products that are on the market that
+   live in one of the disk boot sectors and "take over" the
+   system BIOS INT 13 with an INT 13 that supports the
+   translation.  The biggest problem with this is that the
+   replacement INT 13 BIOS must live someplace in memory.  For
+   DOS based systems, it can usually live at the top of the 640K
+   of memory and DOS is made to think that that part of memory,
+   usually around 8K bytes, does not exist.  But the protected
+   mode OS's don't like this and usually wipe out the driver when
+   they load their kernel.  So if you plan to run multiple OS's
+   on your system, buyer beware!
+
+   Then there is the Windows problem:  the standard FastDisk
+   driver in Windows does *not* support such translation schemes
+   and can not be enabled.  So make sure the driver you
+   purchase also comes with a Windows FastDisk replacement.
+
+   Buyer beware!
+
+### Do I need BIOS or OS drivers to support the ATA-2 data
+### transfer rates?
+
+   Warning:  Read the previous two questions before reading this
+   one.
+
+   Maybe, probably, yes.  The answer to this *very* complex and
+   will be discussed in detail in Part 2. Here is the brief
+   answer...
+
+   If you have a new ATA drive that supports the advanced PIO or
+   DMA data transfer rates (ATA-2 PIO Mode 3 or 4, or, ATA-2 DMA
+   Mode 1 or 2) then you also must have a new ATA host adapter
+   that attaches to the VL-Bus or PCI bus or some other high
+   speed bus (probably a 32-bit bus) in your system.  That host
+   adapter has I/O registers of its own that are used to control
+   its advanced features.  Controlling those advanced features
+   requires software -- either in the system INT 13 BIOS or in a
+   INT 13 BIOS on the host adapter card or in a driver loaded
+   via the boot record or later by your OS.
+
+   Depending on how that host adapter works you may also
+   need a Windows FastDisk replacement in order to use the high
+   speed data transfer modes in Windows.
+
+   Buyer beware!
+
+### I just purchased a new high speed host adapter for my VL-Bus
+### (or PCI bus) system and a new 540MB hard disk.  How do I get
+### full use out of all this new hardware?
+
+   Did you read the previous three questions?
+
+   You need BIOS or driver software and a Windows FastDisk
+   replacement.  These *must* support both CHS translation
+   (because your drive is over 528MB) and the host adapter
+   hardware (to use the high speed data transfer rates).
+
+   Some drivers on the market today use LBA addressing on the
+   ATA interface to get over 528MB.  This may make your disk
+   partition(s) unreadable by another OS.
+
+   Check the hardware and software specifications of the product
+   before you buy it!  Ask lots of questions -- you probably get
+   lots of incorrect or misleading answers -- be prepared for
+   that!  If you plan to run something other than DOS and
+   Windows, especially if you plan a "dual boot" or "boot
+   manager" environment, be real careful.
+
+   Buyer beware!
+
+   OPINION:  I know of only one product that supports all of this
+   new hardware, supports over 528MB *and* supports most of the
+   current OS's that are shipping including several in shipping
+   in beta form.  The product is from a small two person company
+   that is trying to sell the product on an OEM basis and not in
+   the retail market.  - Hale Landis <landis@sugs.tware.com>
+
+/end part 1/
+-- 
+\\===============\\=======================\\
+ \\  Hale Landis  \\      303-548-0567     \\
+ // Niwot, CO USA // landis@sugs.tware.com //
+//===============//=======================//