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ATA is the real name for the mass storage device interface that was frequently called IDE or EIDE in the 1990s and 2000s.
ATA is short for AT Attachment. The AT part is from the IBM PC/AT (1984). ATAPI is short for ATA Packet Interface. ATAPI allows SCSI devices to be attached to the ATA interface.
The ATA interface protocols and command set are widely used in low cost systems. The ATA interface was first standardized in the early 1990s and has been updated many times over the last 25+ years.
ATA comes in two interface favors: Parallel ATA (PATA) and Serial ATA (SATA). Except for Compact Flash (CF) devices, it is basically impossible to purchase new systems or devices that implement PATA. These days nearly all ATA devices implement the SATA interface. However, the ATA command set is implemented nearly the same in both PATA and SATA. But SATA does implement a command queuing scheme call Native Command Queuing (NCQ) that is now widely used by HDD and SSD devices.
An ATA device is a mass storage device that stores data in 512-byte chunks called sectors. These sectors are transferred to/from the device in contiguous blocks of data that are a multiple of 512 bytes. Each sector stored by a device has a unique sector address that is called a Logical Block Address (LBA). The first sector on a device is at LBA 0, the next at LBA 1, etc.
Note that some new ATA device are allowed to have sector sizes other than 512 bytes but these device are generally used only in proprietary systems.
The PI part of ATAPI is Packet Interface. An ATAPI device is really a SCSI device that uses the ATA interface. ATAPI is one of many SCSI physical interfaces. ATAPI is probably the most simple of all the SCSI physical interfaces. In order to implement SCSI over ATA the SCSI Command Data Block (CDB) and data are transmitted over the ATA interface in packets using the Packet command protocol. These packets are generally not 512 bytes in size. An ATAPI device must implement all the ATA signals and most of the ATA command protocols plus the ATAPI Packet command protocol. Unlike ATA, ATAPI devices (SCSI devices) can store data in a variety of formats and block sizes - such as 512 bytes used by many SCSI disk drives, 2048 bytes used for CD/DVD data and 2352 bytes used by CD-DA (digital audio) data (music). Many SCSI commands, such as Inquiry or Request Sense, transfer only a few bytes of data.
PATA is the traditional ATA interface that has been standardized for 25+ years by the ANSI/INCITS ATA-1 through ATA/ATAPI-8 standards. This interface is widely used by low cost disk drives and ATAPI CD/DVD and tape drives. PCMCIA PC Card ATA devices and Compact Flash (CF) devices also use a PATA based interface (for example, the CF TrueIDE interfae).
A Parallel ATA/ATAPI interface can support one or two devices. The devices can ATA or ATAPI or both.
Read more about PATA on the PATA page.
SATA is a serial interface that emulates PATA. SATA has replaced PATA in nearly all low cost storage systems and devices. This includes HDD, SSD and CD/DVD devices.
Around the time that SATA was becoming popular the T13 standards committee separated the ATA command set from the two physical interfaces. Starting with ATA/ATAPI-7 there are separate standards documents for the ATA Command Set (ACS), ATA Parallel Transport (APT) and ATA Serial Transport (AST). The ACS, APT and AST standards now move forward on separate schedules so now there are multiple versions of ACS-x, APT-x and AST-x. However, remember that AST-x is only a document that maps ATA to the SATA-I/O specification that is from the SATA-I/O committee. Also be aware that recently there have been many SCSI features that have been stuffed into ATA with varying degrees of success.
Read more about SATA on the SATA page.
There is a new interface that will probably replace SATA (and SCSI SAS) within a few years. This interface is NVM Express or NVME. SATA and SCSI SAS are limited by the physical I/O architecture to a few thousand I/O commands per second. NVME can achieve millions of I/O commands per second. If you are currently working on SATA products we strongly suggest you start learning about NVME as it has a very good chance of being the primary storage device interface of the future.
T13 is the standards committee that develops and maintains the ATA related ANSI/INCITS standards. Over many years T13 has published the ATA-x, ATA/ATAPI-x, ACS-x, APT-x and AST-x standards. Visit the T13 web site for the latest information on meeting schedules, proposals for the next versions of the many ATA related standards and copies of the draft standards to review.
However, please note that T13 is NOT responsible for the SATA physical interface specfication. That document is published by the SATA-I/O committee.
Here are links to major organizations that publish I/O interface and storage device standards, specifications and other information:
If you are working with ATAPI CD or DVD devices then you also need the SCSI Multi Media Commands (MMC-x) documents. Do not confuse the SCSI MultiMedia Commands (MMC-x) document with the Multi Media Card (MMC) specification. The SCSI MMC-x documents can be found at www.t10.org.
The Berg Software Design web site is a great resouce for finding information, products and services for all I/O interfaces.
If you need serious ATA design or development help for your ATA/ATAPI project, contact Deadline Specialists.
Notice to anyone providing a link to this site: Please provide a link only to http://www.ata-atapi.com. Any other link, including links that specify additional directory or file information, are subject to change and may not work in the future.
Page updated 10 Oct 2015.