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64-646: The Ultra DMA ( Ultra Direct Memory Access , UDMA ) modes were the fastest method used to transfer data through the ATA hard disk interface , usually between the computer and an ATA device. UDMA succeeded Single / Multiword DMA as the interface of choice between ATA devices and the computer. There are eight different UDMA modes, ranging from 0 to 6 for ATA (0 to 7 for CompactFlash ), each with its own timing. Modes faster than UDMA mode 2 require an 80-conductor cable to reduce data settling times , lower impedance and reduce crosstalk . Parallel ATA The standard

128-772: A host adapter interfacing with the rest of the computer system. The remaining connector(s) plug into storage devices, most commonly hard disk drives or optical drives. Each connector has 39 physical pins arranged into two rows (2.54 mm, 1 ⁄ 10 -inch pitch), with a gap or key at pin 20. Earlier connectors may not have that gap, with all 40 pins available. Thus, later cables with the gap filled in are incompatible with earlier connectors, although earlier cables are compatible with later connectors. Round parallel ATA cables (as opposed to ribbon cables) were eventually made available for ' case modders ' for cosmetic reasons, as well as claims of improved computer cooling and were easier to handle; however, only ribbon cables are supported by

192-545: A 20-foot (6.1 m) cable length. The standard channel code for the ST-412 (and ST-506) is MFM with one data bit per transition for a data rate of 5 Mbit/s. The ST-412HP RLL variant averages 1.5 data bits per transition for a data rate of 7.5 Mbit/s. In the ST-506 interface, the drive connects to a controller card with two ribbon cables carrying signals, while a third cable provides power. The two signal cables are

256-437: A 50% increase in capacity and bit rate . The ST-506 HDD was the first 5.25 inch hard disk drive , introduced in 1980 by Shugart Technology (now Seagate Technology ). It stored up to 5 megabytes after formatting (153 cylinders, 4 heads, 32 sectors/track, 256 bytes/sector) and cost US$ 1,500 (equivalent to $ 5,547 in 2023). The similar, 10-megabyte ST-412 HDD was introduced in late 1981 (with 306 cylinders). The ST225

320-426: A cable can perform a read or write operation at one time; therefore, a fast device on the same cable as a slow device under heavy use will find it has to wait for the slow device to complete its task first. However, most modern devices will report write operations as complete once the data is stored in their onboard cache memory, before the data is written to the (slow) magnetic storage. This allows commands to be sent to

384-534: A cable, it should be configured as Device 0 . However, some certain era drives have a special setting called Single for this configuration (Western Digital, in particular). Also, depending on the hardware and software available, a Single drive on a cable will often work reliably even though configured as the Device 1 drive (most often seen where an optical drive is the only device on the secondary ATA interface). The words primary and secondary typically refers to

448-421: A disadvantage: the mechanical drive (called the "head-disk assembly", or HDA) and the controller are effectively fused into a monolithic black box, so that if something goes wrong with the drive, it is nearly impossible to do anything about it—the data is usually irretrievably lost. With a separated controller and disk system like that of the ST-506 interface, sometimes the problem can be resolved by connecting

512-449: A drive to a host with an ATA-5 or earlier interface will limit the usable capacity to the maximum of the interface. Some operating systems, including Windows XP pre-SP1, and Windows 2000 pre-SP3, disable LBA48 by default, requiring the user to take extra steps to use the entire capacity of an ATA drive larger than about 137 gigabytes. Older operating systems, such as Windows 98 , do not support 48-bit LBA at all. However, members of

576-497: A maximum drive capacity of two gigabytes. Later, the first formalized ATA specification used a 28-bit addressing mode through LBA28 , allowing for the addressing of 2 ( 268 435 456 ) sectors (blocks) of 512 bytes each, resulting in a maximum capacity of 128  GiB (137  GB ). ATA-6 introduced 48-bit addressing, increasing the limit to 128 PiB (144 PB ). As a consequence, any ATA drive of capacity larger than about 137 GB must be an ATA-6 or later drive. Connecting such

640-673: A problem in MS-DOS limited the number of heads to 255. This totals to 8 422 686 720 bytes (8032.5 MiB ), commonly referred to as the 8.4 gigabyte barrier. This is again a limit imposed by x86 BIOSes, and not a limit imposed by the ATA interface. It was eventually determined that these size limitations could be overridden with a small program loaded at startup from a hard drive's boot sector. Some hard drive manufacturers, such as Western Digital, started including these override utilities with large hard drives to help overcome these problems. However, if

704-483: A result, many near-synonyms for ATA/ATAPI and its previous incarnations are still in common informal use, in particular Extended IDE (EIDE) and Ultra ATA (UATA). After the introduction of SATA in 2003, the original ATA was renamed to Parallel ATA, or PATA for short. Parallel ATA cables have a maximum allowable length of 18 in (457 mm). Because of this limit, the technology normally appears as an internal computer storage interface. For many years, ATA provided

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768-624: A sound card but ultimately as two physical interfaces embedded in a Southbridge chip on a motherboard. Called the "primary" and "secondary" ATA interfaces, they were assigned to base addresses 0x1F0 and 0x170 on ISA bus systems. They were replaced by SATA interfaces. The first version of what is now called the ATA/ATAPI interface was developed by Western Digital under the name Integrated Drive Electronics (IDE). Together with Compaq (the initial customer), they worked with various disk drive manufacturers to develop and ship early products with

832-411: A third HD SLCT line was shortly added to the design; a fourth was added a not much later by redefining the reduced Write Current signal, needed only by very early drives, as HD SLCT 3. Once the heads are properly positioned and the appropriate head is selected, data is read or written serially through a set of pins in the data cable. The limited bandwidth of the data cable was not an issue at the time and

896-406: A way for the host to determine whether the media is present, and these were not provided in the ATA protocol. ATAPI is a protocol allowing the ATA interface to carry SCSI commands and responses; therefore, all ATAPI devices are actually "speaking SCSI" other than at the electrical interface. The SCSI commands and responses are embedded in "packets" (hence "ATA Packet Interface") for transmission on

960-411: Is MFM, so the absolute signal states are not significant: the data is represented in the timing of the state transitions, like in floppy disk systems. While up to four drives can share a control cable, each drive has its own dedicated data cable connecting it to the hard disk controller (HDC). Most HDCs supported only two drives. The control card translates requests for a particular track and sector from

1024-510: Is a designation that has been primarily used by Western Digital for different speed enhancements to the ATA/ATAPI standards. For example, in 2000 Western Digital published a document describing "Ultra ATA/100", which brought performance improvements for the then-current ATA/ATAPI-5 standard by improving maximum speed of the Parallel ATA interface from 66 to 100 MB/s. Most of Western Digital's changes, along with others, were included in

1088-609: Is defined in the MMC SCSI command set. ATAPI was adopted as part of ATA in INCITS 317-1998, AT Attachment with Packet Interface Extension (ATA/ATAPI-4) . The ATA/ATAPI-4 standard also introduced several " Ultra DMA " transfer modes. These initially supported speeds from 16 to 33 MB/s. In later versions, faster Ultra DMA modes were added, requiring new 80-wire cables to reduce crosstalk. The latest versions of Parallel ATA support up to 133 MB/s. Ultra ATA, abbreviated UATA,

1152-537: Is maintained by the X3/ INCITS committee. It uses the underlying AT Attachment (ATA) and AT Attachment Packet Interface ( ATAPI ) standards. The Parallel ATA standard is the result of a long history of incremental technical development, which began with the original AT Attachment interface, developed for use in early PC AT equipment. The ATA interface itself evolved in several stages from Western Digital 's original Integrated Drive Electronics (IDE) interface. As

1216-401: Is not the factor that limited the performance of the system. However, the unshielded cable can sometimes be susceptible to high levels of noise. Like a floppy drive interface, ST-506 moves the drive head one track at a time with a timed pulse, which cannot occur faster than the stepper motor can move the head. The ST-412 disk drive, among other improvements, added buffered seek capability to

1280-622: The PC/XT from Xebec and for the PC/AT from Western Digital . As a consequence of IBM's endorsement, most of the drives in the 1980s were based on the ST-506. However, the complexity of the controller and cabling led to newer solutions like SCSI , and later, ATA (IDE). A few early SCSI drives were actually ST-506 drives with a SCSI to ST-506 controller on the bottom of the drive. Atari also used Adaptec ACB-4000A SCSI to ST-506 converter inside its own line of SH204/SH205 external ACSI drives. Likewise

1344-537: The ST-506 disk interface and the ST-412 disk interface . Introduced in 1980, the ST-506 was the first 5.25 inch HDD. Its successor, the ST-412, was introduced in 1981 and implemented a refinement to the seek speed, and increased the drive capacity from 5 MB to 10 MB, but was otherwise highly similar. Beginning with its selection as the hard drive subsystem for the original IBM XT disk drive controllers supporting

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1408-500: The Zip drive and SuperDisk drive . Some early ATAPI devices were simply SCSI devices with an ATA/ATAPI to SCSI protocol converter added on. The SCSI commands and responses used by each class of ATAPI device (CD-ROM, tape, etc.) are described in other documents or specifications specific to those device classes and are not within ATA/ATAPI or the T13 committee's purview. One commonly used set

1472-434: The ATA cable. This allows any device class for which a SCSI command set has been defined to be interfaced via ATA/ATAPI. ATAPI devices are also "speaking ATA", as the ATA physical interface and protocol are still being used to send the packets. On the other hand, ATA hard drives and solid state drives do not use ATAPI. ATAPI devices include CD-ROM and DVD-ROM drives, tape drives , and large-capacity floppy drives such as

1536-448: The ATA specifications. A 44-pin variant PATA connector is used for 2.5 inch drives inside laptops. The pins are closer together (2.0 mm pitch) and the connector is physically smaller than the 40-pin connector. The extra pins carry power. ATA's cables have had 40 conductors for most of its history (44 conductors for the smaller form-factor version used for 2.5" drives—the extra four for power), but an 80-conductor version appeared with

1600-760: The ATA/ATAPI-6 standard (2002). Initially, the size of an ATA drive was stored in the system x86 BIOS using a type number (1 through 45) that predefined the C/H/S parameters and also often the landing zone, in which the drive heads are parked while not in use. Later, a "user definable" format called C/H/S or cylinders, heads, sectors was made available. These numbers were important for the earlier ST-506 interface, but were generally meaningless for ATA—the CHS parameters for later ATA large drives often specified impossibly high numbers of heads or sectors that did not actually define

1664-522: The ST-412 interface grew to become ubiquitous in the personal computer industry, The ST-412 interface and its variants were the de facto industry standard for personal computer hard disks until the advent and wider adoption of the IDE or ATA interface in the early 1990s. Both interfaces used MFM encoding; the subsequent extension of the ST-412 interface, the ST-412HP interface, used RLL encoding for

1728-497: The bridge was especially simple in case of an ATA connector being located on an ISA interface card. The integrated controller presented the drive to the host computer as an array of 512-byte blocks with a relatively simple command interface. This relieved the mainboard and interface cards in the host computer of the chores of stepping the disk head arm, moving the head arm in and out, and so on, as had to be done with earlier ST-506 and ESDI hard drives. All of these low-level details of

1792-550: The cable. Cable select is controlled by pin 28. The host adapter grounds this pin; if a device sees that the pin is grounded, it becomes the Device 0 (master) device; if it sees that pin 28 is open, the device becomes the Device 1 (slave) device. This setting is usually chosen by a jumper setting on the drive called "cable select", usually marked CS , which is separate from the Device 0/1 setting. If two drives are configured as Device 0 and Device 1 manually, this configuration does not need to correspond to their position on

1856-409: The cable. Pin 28 is only used to let the drives know their position on the cable; it is not used by the host when communicating with the drives. In other words, the manual master/slave setting using jumpers on the drives takes precedence and allows them to be freely placed on either connector of the ribbon cable. With the 40-conductor cable, it was very common to implement cable select by simply cutting

1920-401: The command interpretation off the controller card and onto the drive itself in order to improve performance is a common feature of later hard drive connection schemes, notably SCSI , with its rich command set, and the storage-focused IDE systems. IDE, in effect, is a system for extending the computer bus so the interface controller can be built into the drive unit rather than being plugged into

1984-469: The computer was booted in some other manner without loading the special utility, the invalid BIOS settings would be used and the drive could either be inaccessible or appear to the operating system to be damaged. Later, an extension to the x86 BIOS disk services called the " Enhanced Disk Drive " (EDD) was made available, which makes it possible to address drives as large as 2 sectors. The first drive interface used 22-bit addressing mode which resulted in

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2048-413: The computer's BIOS and/or operating system . In most personal computers the drives are often designated as "C:" for the Device 0 and "D:" for the Device 1 referring to one active primary partitions on each. The mode that a device must use is often set by a jumper setting on the device itself, which must be manually set to Device 0 ( Master ) or Device 1 ( Slave ). If there is a single device on

2112-420: The computer's backplane. This allows a single "controller" card—really just an interface card—to communicate with multiple dissimilar drives, while it also reduces latency and noise between the controller and drive hardware. Effectively, the roles are reversed: instead of the controller doing almost all of the complex processing and the drive just transferring encoded data between the magnetic disks and

2176-402: The connection cable to the drive. On an IBM PC compatible, CP/M machine, or similar, this was typically a card installed on a motherboard . The interface cards used to connect a parallel ATA drive to, for example, an ISA Slot , are not drive controllers: they are merely bridges between the host bus and the ATA interface . Since the original ATA interface is essentially just a 16-bit ISA bus ,

2240-499: The controller, the drive does almost all of the complex processing and the "controller" just transfers decoded data between the drive and the host system. In these systems, the operational details of the drive, like head selection and seeking, are entirely hidden from the host and handled within the drive's dedicated controller. These became known as "smart" drives, while ST-506–like devices retroactively became known as "dumb". While integrated controllers have many benefits, they also have

2304-526: The disk drive, containing the actual (perhaps very important) data, to another compatible controller. Furthermore, an ST-506 style interface makes it possible and easy not only to replace the controller without throwing away the data, but to get access to the analog data signals from the disk drive and process them through a special data recovery system that may be able to reconstruct data that a normal controller cannot read. Such data recovery techniques are much more difficult to execute on integrated drives, because

2368-488: The era have a SATA hard disk and an optical drive connected to PATA. As of 2007, some PC chipsets , for example the Intel ICH10, had removed support for PATA. Motherboard vendors still wishing to offer Parallel ATA with those chipsets must include an additional interface chip. In more recent computers, the Parallel ATA interface is rarely used even if present, as four or more Serial ATA connectors are usually provided on

2432-577: The goal of remaining software compatible with the existing IBM PC hard drive interface. The first such drives appeared internally in Compaq PCs in 1986 and were first separately offered by Conner Peripherals as the CP342 in June 1987. The term Integrated Drive Electronics refers to the drive controller being integrated into the drive, as opposed to a separate controller situated at the other side of

2496-476: The hard drive in question is also expected to provide good throughput for other tasks at the same time, it probably should not be on the same cable as the optical drive. A drive mode called cable select was described as optional in ATA-1 and has come into fairly widespread use with ATA-5 and later. A drive set to "cable select" automatically configures itself as Device 0 or Device 1 , according to its position on

2560-453: The host system into a sequence of head positioning commands, including setting the direction of head movement, in or out, and sending individual "STEP" commands to move. Four of the control cable pins, "HD SLCT 0" through "HD SLCT 3", allow the selection among up to 16 heads, although only four are available on the two-platter ST-506. The original ST-506/ST-412 interface defined only two HD SLCT lines, providing supporting for only four heads, but

2624-475: The interface. The controller sends the required STEP pulses to the drive as fast as it can receive them. The ST506 disk drive without buffered seek averages 170 ms (similar to a floppy drive or modern optical drive ) while the mechanically very similar ST-412 disk drive with buffered seek averages 85 ms. By the late 1980s, drives with an ST-412 interface were capable of average seek times between 15 and 30 milliseconds. The process of moving portions of

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2688-414: The internal physical layout of the drive at all. From the start, and up to ATA-2, every user had to specify explicitly how large every attached drive was. From ATA-2 on, an "identify drive" command was implemented that can be sent and which will return all drive parameters. Owing to a lack of foresight by motherboard manufacturers, the system BIOS was often hobbled by artificial C/H/S size limitations due to

2752-570: The introduction of the UDMA/66 mode. All of the additional conductors in the new cable are grounds , interleaved with the signal conductors to reduce the effects of capacitive coupling between neighboring signal conductors, reducing crosstalk . Capacitive coupling is more of a problem at higher transfer rates, and this change was necessary to enable the 66 megabytes per second (MB/s) transfer rate of UDMA4 to work reliably. The faster UDMA5 and UDMA6 modes also require 80-conductor cables. Though

2816-548: The manufacturer assuming certain values would never exceed a particular numerical maximum. The first of these BIOS limits occurred when ATA drives reached sizes in excess of 504 MiB , because some motherboard BIOSes would not allow C/H/S values above 1024 cylinders, 16 heads, and 63 sectors. Multiplied by 512 bytes per sector, this totals 528 482 304 bytes which, divided by 1 048 576 bytes per MiB , equals 504 MiB (528 MB ). The second of these BIOS limitations occurred at 1024 cylinders , 256 heads , and 63 sectors , and

2880-442: The mechanical operation of the drive were now handled by the controller on the drive itself. This also eliminated the need to design a single controller that could handle many different types of drives, since the controller could be unique for the drive. The host need only to ask for a particular sector, or block, to be read or written, and either accept the data from the drive or send the data to it. The interface used by these drives

2944-463: The most common and the least expensive interface for this application. It has largely been replaced by SATA in newer systems. The standard was originally conceived as the "AT Bus Attachment", officially called "AT Attachment" and abbreviated "ATA" because its primary feature was a direct connection to the 16-bit ISA bus introduced with the IBM PC/AT . The original ATA specifications published by

3008-551: The motherboard and SATA devices of all types are common. With Western Digital 's withdrawal from the PATA market, hard disk drives with the PATA interface were no longer in production after December 2013 for other than specialty applications. Parallel ATA cables transfer data 16 bits at a time. The traditional cable uses 40-pin female insulation displacement connectors (IDC) attached to a 40- or 80-conductor ribbon cable . Each cable has two or three connectors, one of which plugs into

3072-413: The needed analog signals from the disk are not available at a standard interface and the internal data recording method, sector format, and disk organization of nearly every integrated drive model is different and secret. Many other companies quickly introduced drives using the same connectors and signals, creating a hard drive standard based on the ST-506. IBM chose to use it, acquiring adapter cards for

3136-753: The number of conductors doubled, the number of connector pins and the pinout remain the same as 40-conductor cables, and the external appearance of the connectors is identical. Internally, the connectors are different; the connectors for the 80-conductor cable connect a larger number of ground conductors to the ground pins, while the connectors for the 40-conductor cable connect ground conductors to ground pins one-to-one. 80-conductor cables usually come with three differently colored connectors (blue, black, and gray for controller, master drive, and slave drive respectively) as opposed to uniformly colored 40-conductor cable's connectors (commonly all gray). The gray connector on 80-conductor cables has pin 28 CSEL not connected, making it

3200-408: The other device on the cable, reducing the impact of the "one operation at a time" limit. The impact of this on a system's performance depends on the application. For example, when copying data from an optical drive to a hard drive (such as during software installation), this effect probably will not matter. Such jobs are necessarily limited by the speed of the optical drive no matter where it is. But if

3264-767: The pin 28 wire between the two device connectors; putting the slave Device 1 device at the end of the cable, and the master Device 0 on the middle connector. This arrangement eventually was standardized in later versions. However, it had one drawback: if there is just one master device on a 2-drive cable, using the middle connector, this results in an unused stub of cable, which is undesirable for physical convenience and electrical reasons. The stub causes signal reflections , particularly at higher transfer rates. ST-506 The ST-506 and ST-412 (sometimes written ST506 and ST412 ) were early hard disk drive products introduced by Seagate in 1980 and 1981 respectively, that later became construed as hard disk drive interfaces :

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3328-416: The primary storage device interface for PCs soon after its introduction. In some systems, a third and fourth motherboard interface was provided, allowing up to eight ATA devices to be attached to the motherboard. Often, these additional connectors were implemented by inexpensive RAID controllers. Soon after the introduction of Serial ATA (SATA) in 2003, use of Parallel ATA declined. Some PCs and laptops of

3392-473: The same cable. For all modern ATA host adapters, this is not true, as modern ATA host adapters support independent device timing . This allows each device on the cable to transfer data at its own best speed. Even with earlier adapters without independent timing, this effect applies only to the data transfer phase of a read or write operation. This is caused by the omission of both overlapped and queued feature sets from most parallel ATA products. Only one device on

3456-489: The same time that the ATA-1 standard was adopted, Western Digital introduced drives under a newer name, Enhanced IDE (EIDE). These included most of the features of the forthcoming ATA-2 specification and several additional enhancements. Other manufacturers introduced their own variations of ATA-1 such as "Fast ATA" and "Fast ATA-2". The new version of the ANSI standard, AT Attachment Interface with Extensions ATA-2 (X3.279-1996),

3520-414: The slave position for drives configured cable select. If two devices are attached to a single cable, one must be designated as Device 0 (in the past, commonly designated master ) and the other as Device 1 (in the past, commonly designated as slave ). This distinction is necessary to allow both drives to share the cable without conflict. The Device 0 drive is the drive that usually appears "first" to

3584-480: The standards committees use the name "AT Attachment". The "AT" in the IBM PC/AT referred to "Advanced Technology" so ATA has also been referred to as "Advanced Technology Attachment". When a newer Serial ATA (SATA) was introduced in 2003, the original ATA was renamed to Parallel ATA, or PATA for short. Physical ATA interfaces became a standard component in all PCs, initially on host bus adapters, sometimes on

3648-485: The third-party group MSFN have modified the Windows 98 disk drivers to add unofficial support for 48-bit LBA to Windows 95 OSR2 , Windows 98 , Windows 98 SE and Windows ME . Some 16-bit and 32-bit operating systems supporting LBA48 may still not support disks larger than 2 TiB due to using 32-bit arithmetic only; a limitation also applying to many boot sectors . Parallel ATA (then simply called ATA or IDE) became

3712-402: The two IDE cables, which can have two drives each (primary master, primary slave, secondary master, secondary slave). There are many debates about how much a slow device can impact the performance of a faster device on the same cable. On early ATA host adapters, both devices' data transfers can be constrained to the speed of the slower device, if two devices of different speed capabilities are on

3776-436: The wide 34-pin control cable and the narrow 20-pin data cable . The control cable interface is very similar to the standard Shugart floppy disk interface; like that floppy disk interface, it can support four drives. The data cable carries a read signal and write signal, both as differential binary signals: the two signal states correspond to the two possible differential signal polarities. The data represented by these signals

3840-432: Was approved in 1996. It included most of the features of the manufacturer-specific variants. ATA-2 also was the first to note that devices other than hard drives could be attached to the interface: 3.1.7 Device: Device is a storage peripheral. Traditionally, a device on the ATA interface has been a hard disk drive, but any form of storage device may be placed on the ATA interface provided it adheres to this standard. ATA

3904-558: Was derived from the Shugart Associates SA1000 interface, which was in turn based upon the floppy disk drive interface, thereby making disk controller design relatively easy. The ST-412 interface was adopted by numerous HDD manufacturers such that the interface became a de facto industry standard for disk drives well into the 1990s. The limitations of the ST-412 interface are 5 million transitions per second maximum on data lines, 16 heads, 4 drive units and

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3968-408: Was introduced shortly thereafter with 20 megabytes and half the height. All three used MFM encoding, a widely used coding scheme. A subsequent extension of the ST-412 interface, the ST-412HP interface , used RLL encoding for a 50% increase in capacity and bit rate . The ST-506 drive connected to a computer system through a disk controller . The ST-506 interface between the controller and drive

4032-477: Was originally designed for, and worked only with, hard disk drives and devices that could emulate them. The introduction of ATAPI (ATA Packet Interface) by a group called the Small Form Factor committee (SFF) allowed ATA to be used for a variety of other devices that require functions beyond those necessary for hard disk drives. For example, any removable media device needs a "media eject" command, and

4096-511: Was standardized in 1994 as ANSI standard X3.221-1994, AT Attachment Interface for Disk Drives . After later versions of the standard were developed, this became known as "ATA-1". A short-lived, seldom-used implementation of ATA was created for the IBM XT and similar machines that used the 8-bit version of the ISA bus. It has been referred to as "XT-IDE" , "XTA" or "XT Attachment". In 1994, about

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