Parallel ATA (PATA) is an interface standard for the connection of storage devices such as hard disks, solid-state drives, and CD-ROM drives in computers. The standard is maintained by X3/INCITS committee. It uses the underlying AT Attachment and AT Attachment Packet Interface ( ATA/ATAPI ) standards.
The current Parallel ATA standard is the result of a long history of incremental technical development. ATA/ATAPI is an evolution of the AT Attachment Interface, which was itself evolved in several stages from Western Digital's original Integrated Drive Electronics (IDE) interface. As a result, many near-synonyms for ATA/ATAPI and its previous incarnations exist, including abbreviations such as IDE which are still in common informal use. After the market introduction of Serial ATA in 2003, the original ATA was retroactively renamed Parallel ATA .
Parallel ATA only allows cable lengths up to 18 in (460 mm). Because of this length limit the technology normally appears as an internal computer storage interface. For many years ATA provided the most common and the least expensive interface for this application. By the beginning of 2007, it had largely been replaced by Serial ATA (SATA) in new systems.
History and terminology
The standard was originally conceived as "PC/AT Attachment" as its primary feature was a direct connection to the 16-bit ISA bus introduced with the IBM PC/AT. The name was shortened to "AT Attachment" to avoid possible trademark issues. It is not spelled out as "Advanced Technology" anywhere in current or recent versions of the specification; it is simply "AT Attachment".
IDE and ATA-1
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 Control Data Corporation (who manufactured the hard drive part) and Compaq Computer (into whose systems these drives would initially go), they developed the connector, the signalling protocols, and so on with the goal of remaining software compatible with the existing ST-506 hard drive interface. The first such drives appeared in Compaq PCs in 1986.
The term Integrated Drive Electronics (IDE) refers not just to the connector and interface definition, but also to the fact that the drive controller is integrated into the drive, as opposed to a separate controller on or connected to the motherboard. 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 software 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 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 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 IDE drives 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".
The second ATA interface
Originally, there was only one ATA controller in early PCs, which could support up to two hard drives. At the time in combination with the floppy drive, this was sufficient for most people, and eventually it became common to have two hard drives installed. When the CDROM was developed, many computers were unable to accept them due to already having two hard drives installed. Adding the CDROM would have required removal of one of the drives.
SCSI was available as a CDROM expansion option at the time, but devices with SCSI were more expensive than ATA devices due to the need for a smart controller that is capable of bus arbitration. SCSI typically added US$ 100-300 to the cost of a storage device, in addition to the cost of a SCSI controller.
The less-expensive solution was the addition of the second ATA interface, typically included as an expansion option on a sound card. It was included on the sound card because early business PCs did not include support for more than simple beeps from the internal speaker, and tuneful sound playback was considered unnecessary for early business software. When the CDROM was introduced, it was logical to also add digital audio to the computer at the same time. An older business PC could be upgraded in this manner to meet the Multimedia PC standard for early software packages that used sound and colorful video animation.
The second drive interface initially was not well-defined. It was first introduced with modified controller interfaces specific to certain CDROM drives such as Mitsumi, Sony or Panasonic, and it was common to find early sound cards with two or three separate connectors each designed to match a certain brand of CDROM drive. This evolved into the standard ATA interface for ease of cross-compatibility, though the sound card ATA interface still usually supported only a single CDROM and not hard drives.
This second ATA interface on the sound card eventually evolved into the second motherboard ATA interface which was long included as a standard component in all PCs. For a long period of time, ATA ruled as the primary storage device interface and in some systems a third and fourth motherboard interface was provided (Promise Ultra-100), for up to eight ATA devices attached to the motherboard.
After the introduction of SATA or Serial ATA, use of ATA declined and motherboards began to be shipped with only a single interface, for up to two ATA optical drives, along with two or more SATA connectors for hard drives. Optical drives are now available with SATA, so the ATA interface often goes unused.
EIDE and ATA-2
In 1994, about the same time that the ATA-1 standard was adopted, Western Digital introduced drives under a slightly new 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), 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.
—from , page 2ATAPI
As mentioned in the previous sections ATA was originally designed for and worked only with hard disks and devices that could emulate them. The introduction of ATAPI (ATA Packet Interface) by a group called the Small Form Factor committee allowed ATA to be used for a variety of other devices that require functions beyond those necessary for hard disks. For example, any removable media device needs a "media eject" command, and a way for the host to determine whether the media is present, and these were not provided in the ATA protocol.
The Small Form Factor committee approached this problem by defining ATAPI, the "ATA Packet Interface". ATAPI is actually 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. In fact, some early ATAPI devices were simply SCSI devices with an ATA/ATAPI to SCSI protocol converter added on. The SCSI commands and responses are embedded in "packets" (hence "ATA Packet Interface") for transmission on 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 the Zip drive and SuperDisk drive.
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.
ATAPI was adopted as part of ATA in INCITS 317-1998, AT Attachment with Packet Interface Extension (ATA/ATAPI-4) .
UDMA and ATA-4
The ATA/ATAPI-4 also introduced several "Ultra DMA" transfer modes. These initially supported speeds from 16 MByte/s to 33 MByte/second. In later versions faster Ultra DMA modes were added, requiring a new 80-wire cable to reduce crosstalk. The latest versions of Parallel ATA support up to 133 MByte/s.
Current terminology
The terms "integrated drive electronics" (IDE), "enhanced IDE" and "EIDE" have come to be used interchangeably with ATA (now Parallel ATA). However the terms "IDE" and "EIDE" are at best imprecise. Every ATA drive i
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