A C - 2 5 4 0 WESTERN DIGITAL
NO MORE PRODUCED Native| Translation
------+-----+-----+-----
Form 3.5"/SLIMLINE Cylinders | 1048| |
Capacity form/unform 516/ MB Heads 4| 16| |
Seek time / track 12.0/ 4.0 ms Sector/track | 63| |
Controller IDE / ATA2 FAST/ENHA Precompensation
Cache/Buffer 128 KB SEGMENTED Landing Zone
Data transfer rate MB/S int Bytes/Sector 512
11.100 MB/S ext PIO3
Recording method RLL 1/7 operating | non-operating
-------------+--------------
Supply voltage 5/12 V Temperature *C 5 55 | -40 60
Power: sleep 0.8 W Humidity % 8 80 | 5 95
standby 0.8 W Altitude km -0.300 3.000| -0.300 12.000
idle 3.7 W Shock g 10 | 70
seek 7.0 W Rotation RPM 4500
read/write 3.7 W Acoustic dBA 41
spin-up 11.1 W ECC Bit ON THE FLY,REED SOLOMON
MTBF h 250000
Warranty Month 36
Lift/Lock/Park YES Certificates CSA,FCC,IEC950,TUV,UL1950
**********************************************************************
L A Y O U T
**********************************************************************
WESTERN AC1270/AC2540 TECHNICAL REFERENCE MANUAL S0530 1/94
+---------------------------------------------------------+
| |XX I
| |XX N
| |XX T
| |XX E
| |XX R
| |*X F J2
| |XX A
| |XX C
| |XX E
| |XX
| |XX1
| |6-5 J8
| || |
++LED |2-1
++ |XX J3
| |XX Power
+---------------------------------------------------------+
J2 J8 J3
+39------------------------------------1++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 O|
|o o o o o o o o o o o o o o o o o o o||o o o||4 3 2 1|
--+40------------------------------------2++6-4-2+++-+-+-++----
| | | +12V
(Pin 20 keyed) | | +- GND
| +--- GND
+----- +5V
**********************************************************************
J U M P E R S
**********************************************************************
WESTERN AC1270/AC2540 TECHNICAL REFERENCE MANUAL S0530 1/94
Jumper setting
==============
J8 Master/Slave/Cable Select Configuration
-------------------------------------------
+5-3-1+ Single Drive +5-3-1+ Master Drive
|o o o| Configuration |X o o| Configuration
|o o o| |X o o| (Dual Drives)
+6-4-2+ +6-4-2+
+5-3-1+ Slave Drive +5-3-1+ Cable Select
|o X o| Configuration |o o X| Configuration
|o X o| (Dual Drives) |o o X| (Dual Drives)
+6-4-2+ +6-4-2+
The Caviar can be assigned as either a single, master, or slave
drive.
Dual Installations
------------------
Dual installations require a master/slave drive configuration,
where one drive is designated as the promary (master) drive
and the other is designated as the secondary (slave) drive. The
Caviar drive is compatible in dual installations with other
intelligent drives that supports a master/slave configuration.
If your installation requires the use of an adapter card, it is
useful to know that you may also be able to connect your floppy
drive(s) to the adapter card.
Single Drive Mode
-----------------
If you are installing the Caviar drive as the only intelligent drive
in the system, you do not need install jumpers on the J8 connector.
This is considered a standard single drive installation, and no
jumpers are required. Note that even with no jumper installed, the
Caviar checks the DRIVE ACTIVE/SLAVE PRESENT (DASP) signal to de-
termine if a slave intelligent drive is present.
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 J8 connector need to be configured for
the dual installation.
Master Drive Mode
-----------------
To designate the drive as the master, place a jumper shunt on pins
5-6. With the Caviar configured as the master drive, the Caviar
assumes that a slave drive is present. The jumper on pins 5-6 is
optional if the slave drive follows the same protocol (Common Access
Method AT Bus Attachment) as the Caviar.
Slave Drive Mode
----------------
To designate the drive as the slave, place a jumper shunt on pins
3-4. When the Caviar is configured as the slave drive, the Caviar
delays spin up for three seconds after powerup reset. This feature
prevents overloading of the power supply during power-up.
Cable Select (CSEL)
-------------------
Caviar also supports the CSEL signal on the drive cable as a drive
address selection. Place a jumper shunt on pins 1-2 to enable this
option. When enabled, the drive address is 0 (Master) if CSEL is low
or 1 (Slave) if CSEL is high.
Do not install the CSEL jumper shunt when installing the Caviar drive
in systems that do not support the CSEL feature.
**********************************************************************
I N S T A L L
**********************************************************************
WESTERN AC1270/AC2540 TECHNICAL REFERENCE MANUAL S0530 1/94
Notes of Installation
=====================
Installation direction
----------------------
horizontally vertically
+-----------------+ +--+ +--+
| | | +-----+ +-----+ |
| | | | | | | |
+-+-----------------+-+ | | | | | |
+---------------------+ | | | | | |
| | | | | |
| | | | | |
+---------------------+ | +-----+ +-----+ |
+-+-----------------+-+ +--+ +--+
| |
| |
+-----------------+
The drive will operate in all axis (6 directions).
Orientation
-----------
The Caviar can be mounted in the X, Y, or Z axis depending upon the
physical design of your system.
Determining Your Configuration
------------------------------
You can configure the Caviar in one of two ways:
1. The drive is cabled directly to a 40-pin connector on the mother-
board, or
2. The drive is cabled to an adapter card mounted in one of the
expansion slots in the computer.
Both configurations use a 40-pin host interface cable.
If you are using the Caiar drive as one of two hard disk drives in
the computer (dual installation), you may use either configuration.
In dual installations, you must use a 40-pin host interface cable
with three connectors and daisy-chain the two drives to the mother-
board or adapter card.
Mounting the Drive
------------------
For dual installations, it is usually easier to completely install
one intelligent drive in the lower position first. The order of
intelligent drives is unimportant if you are using to Western Digital
drives. As explained previously, one must be jumpered as the master
drive and the other as the slave drive. When installation is complete
he drives are daisy-chained together.
Cabling and Installation Steps
------------------------------
Make sure your interface cable is no longer than 18 inches to
minimize the noise which is induced on the data and control buses.
Also, if you are connecting two drives together, you need a daisy-
chain cable that has three 40-pin connectors.
Caution: You may damage the Caviar drive if the interface cable is
not connected properly. To prevent incorrect connection, use a cable
that has keyed connectors at both the drive and host ends. Pin 20
has been removed from J2 connector. The female connector on the
interface cable shoul have a plug position 20 to prevent incorrect
connection. Make sure that pin 1 on the cable is connected to pin 1
on the connectors.
Mounting Screws
---------------
Mount the caviar drive bay using four 6-32 screws. Be sure to use the
correct size screws. Do not install the screws past six threads
(3/16 inch). Screws that are too long will damage the Caviar drive.
Power Connectors and Cables
---------------------------
Power Connector: 4-pin AMP (P/N 84069-1) or equivalent
Mating Connector: Body AMP 1-480424-0 or equivalent
Pins AMP 60619-4 or equivalent
Power Cable Wire Gauge 18 AWG
Universal Translation
---------------------
The Caviar implements 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. Caviar supports universal translation, therefore, any
valid combination of cylinder, head and SPT can be assigned to the
drive, as long as the total number of sectors is not greater than the
physical limits. The product of the cylinder, head and sectors/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 are:
AC1270 - 528,192
AC2540 - 1,056,384
Each sector consists of 512 bytes.
The minimum values for any translation parameter is one. The maximum
value for any translation parameter is as follows:
Sectors/Track - 255
Heads - 16
Cylinders/Drive - 2048
**********************************************************************
F E A T U R E S
**********************************************************************
WESTERN AC1270/AC2540 TECHNICAL REFERENCE MANUAL S0530 1/94
Zoned Recording
---------------
The AC1270, and AC2540 drives employ Zoned Recording to in-
crease the data density on the outer tracks of the drive. The outer-
most tracks contain 71% more sectors than the innermost tracks,
thereby increasing the total capacity of the drive.
Advanced Defect Management
--------------------------
The Caviar is preformatted (low-level) at the factory and comes with
a full complement of defect management functions. Extensively tested
during the manufacturing process, media defects found during
intelligent burn in are mapped out with Western Digital's high
performance defect management technique. No modifications are
required before installation.
Embedded Servo Control
----------------------
The Caviar festures an embedded servo concept as the means of
providing sampled position feedback information to the head position
servo system. Servo bursts are located along a radial path from the
disk center,ensuring that head positioning data occurs at constant
intervals. This high sampling rate supports the high frequency
servo bandwidth required for fast access times as well as highly
accurate head positioning. The embedded servo concept provides the
means of generating accurate feedback information without requiring
a full data surface as would a dedicated servo control concept.
Seek Time
---------
Average Seek read 11 Milliseconds
write 13 Milliseconds
Track-to-Track Seek 4 Milliseconds
Maximum Seek 25 Milliseconds
Index Pulse Period 13.33 Milliseconds
Average Latency 6.67 Milliseconds
Defect Management
-----------------
Every Caviar undergoes factory-level intelligent burn in, which
thoroughly tests for and maps out defective sectors on the media
before the drive leaves the manufacturing facility. Following the
factory tests, a primary defect list is created. The list contains
the sector cylinder and head numbers for all defects.
Defects managed at the factory are sector slipped. Grown defects that
can occur in the field are handled by realocation to spare sectors on
the inner cylinders of the drive.
Format Characteristics
----------------------
In order to be compatible with existing industry standard defect
management utility programs, the Caviar supports logical format. When
the host issues the Format Track command, the Caviar performs a
logical version of this command in response to the host's interleave
table request for good and bad sector marking or assign/unassign the
sector to/from an alternate sector.
If the host issues the Format Track Command during normal operating
modes, the data fields of the specified track are filled with a data
pattern of all zeros. The Format Track Command can be used to mark/
unmark bad sectors, and reassign unrelicated sectors.
**********************************************************************
G E N E R A L
**********************************************************************
WESTERN ENHANCED EIDE
Enhanced IDE Backgrounder
=========================
The Computer Market and the IDE Interface:
------------------------------------------
The computer marketplace is segmented into various classes of
machines divided by user expectations in terms of cost, performance,
compatibility and ease-of-use. The largest distinct segment today is
the personal computer market, characterized by single- user products
supporting a broad user base. The usage of these machines in business
and home environments has dictated an emphasis on cost and
compatibility. Historically, cost and compatibility in the personal
computer marketplace have been more important to mainstream users
than very high performance. The PC user has simply not been willing
to bear the added cost or potential lack of compatibility that
highest performance solutions imply.
Given this criteria, the mainstream volume personal computer market
has standardized on the IDE interface for its primary storage needs.
The success of the IDE interface in the PC market has resulted
primarily from a perfect match between IDE's offerings and the
requirements of the market it serves. Specifically, its low cost of
connection, compatibility, and ease-of-use, compared to alternative
interfaces such as the Small Computer System Interface (SCSI), have
been essential attributes in satisfying an expansive price-sensitive
user group. In addition, because of the broad user base it serves,
the personal computer market has traditionally required only hard
disk support to meet its mass storage requirements. IDE has therefore
evolved as a drive-only interface.
Increasing Need for Performance and Connectivity Flexibility:
-------------------------------------------------------------
As the personal computer market matures, it continues to display an
increased emphasis on enhanced performance and connectivity
capabilities, while maintaining its focus on cost, compatibility and
ease-of-use. The market criteria has therefore grown to include
higher performance attributes without sacrificing the needs of its
price sensitive customers. It is in the realm of higher performance
characteristics and connectivity that today's traditional IDE
interface faces challenges. Other existing interfaces, such as SCSI,
provide greater flexibility and performance options to meet these
requirements, while failing to provide IDE's benefits of
compatibility, cost and ease-of-use.
Western Digital's Enhanced IDE technology addresses the performance
and connectivity challenges facing the IDE interface. Enhanced IDE is
designed to extend the attributes of the IDE interface so that its
characteristics more effectively match the new requirements of the
evolving personal computer market, without forfeiting its traditional
benefits.
Western Digital and the IDE Interface - Building upon Expertise:
----------------------------------------------------------------
Western Digital's Enhanced IDE technology evolves from the company's
storage expertise within the personal computer marketplace. In 1984,
Western Digital developed the WD1002 floppy and ST506 interface hard
disk controller that IBM utilized in their PC/AT systems. The success
of the PC/AT architecture led to the massive growth of the IBM PC/AT
compatible market. This dramatic growth was in part fueled by WD1002
compatible hard disk controllers and later by Western Digital's
standard-setting WD1003 series of AT controllers.
As the market expanded and became more price sensitive, Western
Digital defined the need for integration of the AT controller
electronics within the disk drive. By working with Compaq Computer
Corporation, Western Digital again drove the technology by proposing
the IDE (Integrated Drive Electronics) interface which was
implemented in the industry's first IDE drive in 1986. The disk
drives used in personal computers have standardized around IDE since
this introduction.
ATAPI Specification:
--------------------
Now, Western Digital continues to lead the industry with its IDE
interface expertise via Enhanced IDE, an approach that expands upon
the existing attributes of the IDE interface and extends its usage
into more demanding environments. Enhanced IDE not only incorporates
high speed host transfer capabilities, support of high capacity disk
drives, and multiple device connectivity, but it also includes
non-disk peripheral support via the Western Digital authored ATAPI
(AT Attachment Packet Interface) specification. This
enhanced IDE-ATA specification enables connectivity of non-disk
peripherals such as CD-ROM and tape drives. The Western Digital
defined ATAPI specification, with participation and endorsement by
key market-making OEMS, CD-ROM suppliers and operating system
suppliers, is yet another example of Western Digital's commitment to
the evolution of the IDE interface.
Enhanced IDE:
-------------
Enhanced IDE removes many of the existing limitations and issues
associated with the current IDE interface. Removal of these
limitations enables IDE to grow with the industry's increased mass
storage requirements without sacrificing its key cost, compatibility
and ease-of- use attributes. The historical limitations of IDE
relative to other interfaces, such as SCSI, have not threatened IDE's
dominance of the PC marketplace to date. Upcoming personal computer
systems, architected around high performance processors, more complex
operating systems, and more demanding software applications, have
developed storage requirements beyond the realm of today's IDE
capabilities, challenging IDE's dominant role in the PC market.
Specifically, the IDE interface is less flexible and limited in key
areas of performance and connectivity relative to the SCSI interface:
The IDE interface supports two disk drives. The SCSI interface
supports multiple devices includingprinters, CD-ROM, tape drives
as well as hard disk drives.
The IDE interface is limited to 528MB hard disk capacity as a
result of the Int 13h BIOS interface used to access IDE
drives. The SCSI interface is not limited in capacity. The
IDE interface typically offers 2-3MB/sec host transfer rates
on standard ISA bus architected machines. The SCSI interface
offers 10MB/sec FAST transfers and up to 20MB/sec FAST/WIDE
host throughput.
Western Digital's Enhanced IDE technology offers solutions to the
existing constraints associated with the current IDE interface such
as capacity limitations, slower host transfers, and connectivity
issues associated with the IDE interface and thereby enables a cost
effective, compatible, and easy-to-use interface solution for the
next generation of personal computers.
Components of Enhanced IDE:
---------------------------
Enhanced IDE focuses on removing four primary limitations of the
existing IDE interface. These include:
Removal of the 528MB capacity barrier
Breaking the IDE transfer bottleneck
Supporting multiple IDE devices
Enabling non-disk peripheral connectivity, such as CD-ROM
Below, each of these limitations is discussed and resolved in detail.
Removal of Capacity Limitations
-------------------------------
A barrier in implementing IDE disk drives greater than 528MB exists
in today's standard AT system BIOS. This barrier is based on
historical reasons dating from the development of the original AT
machine in 1984. Specifically, it is a limitation of the combined
Interrupt 13 software interface and the IDE interface. The goal is to
change the system BIOS such that this barrier no longer exists,
thereby enabling the usage of high capacity IDE disk drives. Western
Digitial's specification for removing the 528MB barrier is a simple
yet effective method for implementation by BIOS suppliers and system
manufactures who write their own BIOS.
The capacity limitation exists due to the number of bits allocated
for specifying the cylinder, head, and sector address information at
both the Int 13h interface level and at the IDE interface level.
Because Int 13h and IDE specify differing values, combining these two
interfaces produces an artificial 528MB barrier as shown below:
BIOS IDE
---------------------------------------------------------------
Limitation Max Sectors/Track 63 225 63
Number of Heads 255 16 16
Number of Cylinders 1024 65536 1024
Maximum Capacity 8.4GB 136.9GB 528MB
Two solutions exist that resolve the existing 528MB barrier problem.
The first method is to have the BIOS translate the CHS address at the
13h interface to the CHS parameters being used at the drive
interface. The Enhanced IDE proposal to break the 528MB barrier is to
utilize the second method of modifying the Int 13h BIOS so that it
translates the cylinder, head, sector information passed to it via
Int 13 into a 28 bit Logical Block Address (LBA). The LBA solution is
believed to be the best method of breaking the 528MB barrier because
it provides a clean and efficient way for future operating system
drivers to access IDE drives.
The LBA translation is loaded into the drive's task file registers.
Bit 6 of the drive's SDH register is set to indicate to the drive's
firmware that it should interpret the information in its task file
registers as LBA rather than cylinder, head and sector information.
This scheme will allow for the full use of all of the bits allocated
for CHS information at the Int 13h interface, thereby supporting up
to 8.4GB.
Using a logical block addressing scheme is attractive primarily
because it is 100 percent compatible with BIOS Int 13 and allows for
reduced overhead, producing higher performance. The logical block
addressing scheme provides the compatibility essential for personal
computer usage as well as enables the implementation of higher
capacity disk drives required for high performance machines.
Western Digital's LBA scheme has been successfully demonstrated by
key system manufacturers writing their own BIOS and by those working
in conjunction with their BIOS suppliers. Systems shipping in
calendar Q4, 1993 will implement this scheme with the Western Digital
Caviar AC2540.
Bypassing the AT-IDE Host Transfer Bottleneck:
----------------------------------------------
The ISA bus capabilities are designed to sustain host throughput data
rates of roughly 2-3MB/sec. Relative to SCSI host transfer rates of
5MB, 10MB, and 20MB/sec, the ISA bus is painfully slow for higher
performance applications. Because AT personal computers did not
necessarily demand the higher performance obtained by their
workstation or file server counterparts, 2-3MB/sec wasn't considered
a limiting factor. In addition, the ISA bus capabilities of 2-3MB/sec
did not present a throughput problem because data rates coming off
the media were roughly only 5Mbits/sec, and not a challenge to the
host throughput.
As disk drive areal density technologies progressed, media data rates
began to exceed the 2-3MB/sec ISA host throughput. Buffering either
on the system or the drive was necessary to maintain performance. The
industry's most recent drive offerings far exceed the ISA bus host
throughput by providing media data rates of up to 48Mbit/sec. Due to
these factors, increased buffering is not a cost effective
alternative to faster host throughput.
Fast PIO Transfers:
-------------------
Other peripherals within the computer, such as video, resolved their
throughput problems via local bus architectures providing a potential
path for improved performance. IDE local bus solutions, leveraged
from the success of video local bus, began appearing in 1992, as a
way to enhance data throughput. These solutions mapped the IDE data
port to the local bus, bypassing the ISA bus and enabling the
maximization of throughput from the media to the drive buffer, on to
the host. These solutions were still not competitive with Fast SCSI
(10MB/sec) due to the "blind" transfer nature of the PIO transfers.
"Blind PIO" transfers indicate host control of data throughput with
the host requesting data (master) and the drive responding (slave).
With blind PIO transfers, the host is unaware or "blind" when
buffered drive bandwidth is 100% available for host transfers.
Because there are cases when only a percentage of bandwidth is
available, blind PIO host requests for data from the drive are based
on the worst case bandwidth availability. This means that even when
the ISA bottleneck is bypassed by connection directly to the local
bus, inability to utilize 100% drive bandwidth prevents full
optimization of host throughput.
Enhanced IDE incorporates an operation called "Flow Control Using
IORDY" (I/O Channel Ready) which allows the drive to "throttle" the
host when necessary and enable burst transfers to take advantage of
100% of the bandwidth. Flow Control thereby gives control of the data
transfer to the drive and eliminates the inefficiencies of blind PIO
by setting the host to maximum drive bandwidth support. This means
that when 100% drive bandwidth is available, the drive will take
control and transfer data to the host.
This operation, based on approved Mode 3 PIO timings of 180ns cycle
times from the Small Form Factor Committee, supports transfer rates
up to 11MB/sec competitive with FAST SCSI solutions. Flow Control is
enabled on the drive by the host issuing a Set Features command, so
that both the host and drive side support this operation. Western
Digital's 540MB drives (shipping beginning September, 1993) support
flow control using IORDY and will be implemented into machines that
take advantage of this feature via low cost ASICS whose functionality
will later be incorporated into core logic chipset solutions.
DMA Transfers
--------------
Although PIO is the standard transfer method supported by the
industry and presents no incompatibility issues (see footnote),
another transfer option exists that provides incremental transfer
benefits beyond PIO. Direct Memory Access (DMA) is based on data
transfer directly to memory rather than via the CPU. DMA transfers
are "throttled" and therefore have historically offered the benefit
of maximizing data throughput. The throttling mechanism associated
with DMA has historically enabled improved data transfers relative to
standard PIO.
Type B DMA was defined with the arrival of Extended Industry Standard
Architecture (EISA), and is specified at 4.0MB/sec transfer rates
offering an advantage to the standard 2-3MB/sec PIO data rates.
Although this is an improvement to the standard ISA bus timings, Type
B DMA remains uncompetitive with FAST SCSI timings of 10MB/sec.
With the advent of local bus solutions, a new DMA transfer has
emerged in conjuction with PCI. Type F DMA is defined to support
8.33MB/sec and 6.67MB/sec data rates, a large improvement over Type B
DMA. In conjunction with chipsets capable of supporting 6.67MB and
8.33MB/sec data rates, the Small Form Factor Committee has approved a
new multiword DMA Mode 1 timing specification of a 150ns cycle time.
This enables DMA transfers up to 13MB/sec for future data rate
improvement by allowing multiple words to be transferred for any
given request command. PCI chip sets will be shipping with both EISA
(Type B) and ISA (Type F) configurations in the calendar CYQ4'1993
time frame.
PIO versus DMA:
---------------
The disadvantage of DMA transfer operations is that the PC/AT hard
disk controller and later IDE, evolved around PIO data transfers.
Therefore, the system Int 13h BIOS and the embedded operating system
device drivers have supported PIO transfers versus DMA transfers.
This simply means that BIOS changes and external device drivers are
necessary to achieve the incremental performance that DMA offers.
Western Digital's Enhanced IDE program supports system manufacturers'
choice of either PIO transfers via Flow control with IORDY for Mode 3
PIO data rates or DMA transfers (both Type B and Type F) via the
development of external DMA device drivers supporting Western Digital
hard disk drives. Product platforms based on both high speed transfer
options will be in production in calendar fourth quarter 1993.
Supporting Multiple IDE Devices:
--------------------------------
The original IBM PC/AT defined support for two hard disk controllers
and allowed support for up to four disk drives via a primary and
secondary controller. The original BIOS and operating system drivers,
however, only supported the primary controller, limiting the standard
PC configuration to two disk drives. Today's operating systems now
offer both primary and secondary controller support providing an
opportunity to extend peripheral attachment capabilities with IDE.
The addition of a second connector via a hardware change is a simple,
low cost solution that allows for multiple IDE peripheral
connectivity.
The cost of a second IDE connector is less than $1.00. Most core
logic and Super I/O devices have already integrated the capability to
support either the primary or secondary address decode logic and
therefore the cost of the secondary port is simply the 40 pin
connector and surrounding transceivers and resistors. For $1.00, dual
IDE connectors offer support for four IDE devices and satisfy the
expansion needs of the majority of the mainstream personal computer
market, a very cost effective alternative to connectivity via SCSI.
Western Digital's Enhanced IDE program works with system
manufacturers to understand the BIOS implications of a secondary
channel for support of two additional IDE devices. The BIOS must be
able to determine the physical location of the drive based on the Int
13h drive number . Since DOS 3.0 and later will support up to seven
disk drives, only the system BIOS Interrupt 13h needs to be modified
to support primary and secondary IDE. Windows 3.1 accesses the disk
via Interrupt 13h calls to the BIOS. Again, all that is required is
modification to the system BIOS to support dual channel IDE. IBM OS/2
2.0 and 2.1 as well as MS/IBM OS/2 1.31 all support four IDE drives
on dual IDE connectors via their drivers. Netware is hardcoded to
support four IDE connectors or 8 IDE devices. Dual channel IDE
support will be in the final release of Windows NT.
Dual channel IDE not only enables the cost effective and easy
implementation to support multiple disk drives, it presents the
opportunity to expand IDE into non-disk peripheral support. A slow
speed channel and a high speed channel can be developed for efficient
implementation of storage solutions via high performance hard disk
drives and mass data storage vehicles such as CD-ROM and tape drives.
Enabling Non-disk Peripheral Connectivity:
------------------------------------------
The upcoming high performance desktop machines are demanding
additional storage peripheral support beyond hard disk drives.
Specifically, CD-ROM and tape drives will demonstrate rapid unit
growth rates as these peripherals become a more standard part of the
desktop's configuration. Today's CD- ROMs and tape drives have
multiple interfaces that present compatibility and performance
issues. Development of a standard IDE interface for both CD-ROMs and
tape drives solves cost, compatibility, performance, and ease-of-use
issues in conjunction with enabling the attachment of non-disk
devices via the IDE interface.
Western Digital, with its AT interface expertise, has taken the
leadership position in expanding the IDE interface to support
non-disk peripherals by authoring the AT Attachment Packet Interface
(ATAPI). The specification defines a standard method for interfacing
to a CD-ROM drive (and other non-disk devices) utilizing the existing
ATA host computer hardware and cabling. ATAPI supplements the
definitions of an ATA mass storage peripheral found in the ATA
specification and is compatible with existing ATA hardware without
any changes or additional pins.
Traditional computer architecture has used a register based transport
mechanism. Modern architectures now use packet-based transport
mechanisms. ATAPI is an enhancement to IDE that follows this trend.
Benefits of including a packet-based scheme means adding very few IDE
operation codes. The ATAPI specification adds only a single new IDE
command to obtain functionality and only two additional new IDE
commands to address compatibility. Once a packet-based interface was
defined, the next issue was deciding what command packets definitions
to utilize. Given widespread support for SCSI within peripherals and
within existing operating systems, it was decided to derive ATAPI
command packets from SCSI to minimize development time and expense.
The ATAPI specification is being reviewed by an industry working
group that consists of market-making system manufacturers, CD-ROM
suppliers, silicon designers, BIOS developers, and Western Digital.
The objective is to finalize the ATAPI specification around which
these companies will design and manufacture products for the personal
computer industry. Although the exact strategy has yet to be decided
upon, the document will eventually be submitted to a standards
committee for adoption.
Putting it All Together
------------------------
Support for four IDE devices
Fast IDE port for disk drives
Slow IDE port for CD-ROMs and tape
True plug and play
Lowest cost of connection
Overlapped I/Os for higher performance
The Big Picture:
----------------
It is clear that the mass storage needs of the personal computer
industry are expanding to include higher performance and connectivity
requirements. Enhanced IDE was developed in response to these
requirements. The industry is already embracing Enhanced IDE and its
elements of improved functionality, performance, and connectivity by
introducing products in the calendar fourth quarter of 1993. These
products include BIOS support for >528MB IDE hard disk drives, the
shipment of >528MB IDE drives themselves, silicon and controller
products supporting fast PIO and DMA transfers, and hardware
supporting dual channel IDE for multiple device connectivity.
Momentum in the development of the industry's first standard IDE non-
disk peripherals is well underway with the industry's first IDE
CD-ROMs anticipated to ship in calendar first quarter 1994.
SCSI and IDE Scorecard:
The industry activity backed by real Enhanced IDE products means that
IDE has met the challenge in addressing the industry's new
requirements. IDE's cost effectiveness and compatibility advantages,
matched now with high performance and connectivity attributes make it
a solid storage interface solution well into the future. A new
comparison of the AT/SCSI scorecard reveals the successful approach
of Enhanced IDE:
Standard AT Interface
--------------------
* The IDE interface supports two disk drives.
* IDE is a hard disk only interface.
* The IDE interface is limited to 528MB hard disk capacity as as
result of the Int 13h BIOS interface used to access IDE drives.
* The IDE interface is typically limited to 2-3MB/sec host
throughput.
With Enhanced IDE
-----------------
* The IDE interface supports four IDE devices with dual channel IDE
and more with multiple IDE connectors.
* The IDE interface supports non-disk peripherals such as IDE CD-ROM,
IDE Tape.
* With LBA, the IDE interface supports up to 8.4G of hard disk
capacity.
* With Mode 3 PIO and multiword DMA mode 1, data transfer rates with
IDE drives can be from 11MB/sec up to 13MB/sec.
With Enhanced IDE, the IDE interface has become a mass storage
interface for personal computers and is no longer simply a disk drive
interface. Enhanced IDE complements SCSI in that it remains primarily
an internal interface solution with SCSI as an external interface
solution.
Western Digital is a registered trademark of Western Digital
Corporation. All marks mentioned herein belong to other companies.
PIO transfers are based on using the CPU to perform the data transfer
(Processor I/O) and is the standard transfer method supported within
all existing BIOS and all embedded operating system device drivers.
PIO implies compatibility with existing BIOS/OS and therefore does
not require added device driver support for operation.