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The Brief History of ATA and ATAPI

Marketing hype says that Western Digital was the sole inventor of the ATA (IDE) interface.


Western Digital was just one of several companies that designed what we now know as the ATA interface. Here is the real story...

It all starts in about 1986 with CAM ATA...


The interface that we now call ATA was originally developed in 1986 by three companies: 1) a division of Control Data Corporation (CDC) called Imprimis, 2) Western Digital, and 3) Compaq Computer. Back in those days Imprimis was a major disk drive supplier and Western Digital was a major silicon supplier. Western Digital developed the hard disk controller chip that IBM used in the PC/AT computers starting in 1984.

Initially this new interface, called IDE by some people and AT Attachment (ATA) by other people, was used only by Compaq. Most of the disk drives Compaq was using were the new 3.5-inch drives made by a disk drive company named Conner Peripherals. Compaq didn't use many Imprimis drives because Imprimis was not making 3.5-inch drives yet. ATA/IDE became really popular when Conner Peripherals starting selling its drives in retail stores and when all the other major disk drive companies started making ATA/IDE drives.

The first document describing this interface was submitted to the Common Access Method (CAM) committee on 01 April 1989 (no, it was not an April Fool's joke(?)). The Common Access Method committee was developing what later became the SCSI CAM standard that still exists today. Read about the very beginnings of ATA in this short History of CAM ATA written by the editor of the original CAM ATA document!

Fast forward a few years... In 1989 Seagate purchased Imprimis from Control Data. And then in 1995 Seagate purchased Conner Peripherals. By the mid 1990s Western Digital had become a major disk drive supplier.

The ATA/ATAPI Standards

The ATA standard (the real IDE/EIDE standard) comes in several flavors: ATA (also called ATA-1), ATA-2, ATA-3 and ATA/ATAPI-4, ATA/ATAPI-5, ATA/ATAPI-6 and ATA/ATAPI- 7 and then ATA-8. Each of these is described below.

Is it X3 or INCITS?

Note that the organization that sponsors the various technical committees for computer standards changed its name from X3 to INCITS in the late 1990s. This has changed the names of the technical committees too. For example, the committee X3T13 is now known as INCITS T13. And it also changes the way the document numbers for new standards are assigned. The old way was X3.nnn-year. The new way is INCITS.nnn-year.

ATA (aka ATA-1 or IDE)

ATA (ATA-1) is ANSI document number X3.221-1994.

ATA is the real standard for what is widely known as IDE.

In 1999, at the recommendation of INCITS T13, ATA (ATA-1) was withdrawn as an ANSI standard.

ATA-2 (aka EIDE, FASTATA, ...)

ATA-2 is ANSI document number X3.279-1996.

ATA-2 is the real standard for what is widely known as EIDE. ATA-2 introduced higher speed data transfer modes: PIO Modes 3 and 4 plus Multword DMA Mode 1 and 2. These modes allow the ATA interface to run data transfers up to about 16MB/second.

Is it IDE, EIDE, FASTATA, ... ?

So starting with ATA-2 what do we call this I/O interface?

Most companies now call the interface by its proper name: ATA or ATAPI.

The other names are all the result of marketing hype from one or more of the companies making ATA products.

IDE was used by Conner Peripherals, Compaq and Western Digital starting back in 1986-1987. It continues to be widely used as the alternate name for ATA.

EIDE was first used by Western Digital to hype a new line of disk drives back in 1993 or 1994. These were ATA-2 compatible drives that supported the new PIO modes 3 and 4 data transfer timings. Western Digital was trying to establish itself as a major disk drive supplier in those days. Western Digital continues to use EIDE to describe their products even though the ATA interface has progressed well beyond the capabilities of ATA-2. Western Digital just keeps redefining what they mean by EIDE!

FASTATA and FASTATA-2 were used by Seagate and Quantum in marketing programs that were intended to counter the Western Digital EIDE marketing hype back in 1993 or 1994. It appears that by 1998 both Seagate and Quantum had stopped using these alternative names for ATA products.

In 1999 some companies started to use ULTRA ATA to describe products that support the ATA/ATAPI-4 Ultra DMA 33 data transfer protocols. We will have to wait and see what cute name the disk drive marketing folks come up with to sell ATA/ATAPI-5's Ultra DMA 66 data transfer protocols.

Bottom line: These are all just alternative names for ATA used mostly by marketing departments to make it sound like they have a REALLY NEW AND IMPROVED product that is somehow different from the competition's product.


An IDE, EIDE, FASTATA or ULTRA ATA device is really an ATA (or ATAPI) device and all such devices are generally compatible with each other and can be used in the same system and even on the same ATA cable. Of course there are exceptions (devices that don't conform to the ATA or ATA/ATAPI standards).


ATA-3 is ANSI document number X3.298-1997.

ATA-3 introduces some new features of questionable value: SMART and Security. Note that ATA-3 does NOT introduce any new (faster) PIO or DMA data transfer modes (there is no such thing as PIO mode 5!).

ATAPI? What is that?

ATAPI is the real name of the CD-ROM (EIDE CD-ROM) and tape (ATAPI tape or EIDE tape) interface. This interface was originally developed by a group of CD-ROM companies with lots of help from Western Digial and Oak Technology.

ATAPI did not start as an ANSI standard. It was a specification published by the Small Form Factor (SFF) committee. SFF is an ad hoc disk drive industry committtee that usually concerns itself with things like connectors, the location of mounting holes and other physical configuration stuff. The original SFF document for ATAPI was called SFF-8020 (now called INF-8020).

NOTE: SFF-8020 (INF-8020) is very OBSOLETE and should not be used! The correct documents to use for ATAPI are ATA/ATAPI-4 (or higher) and SCSI MMC-2 or higher.

ATAPI introduced a new command execution protocol for use on the ATA interface so that these new CD-ROM and tape drives could, in theory, be on the same ATA cable with an ATA hard disk drive. Basically, the ATAPI Packet command, command code A0H, is used to send what looks like a SCSI CDB across the ATA interface. The actual data transfer (from/to the device media) is done using the ATA PIO or DMA protocols.

If you want to know what "SCSI like" commands are accepted by ATAPI devices then you should probably read the appropriate SCSI-3 document(s) for back ground information. Then get the appropriate SFF document for the ATAPI device type, for example, SFF-8070 describes the ATAPI super floppy "SCSI like" command set. There are many of these ATAPI "command set" documents floating around the industry today and even keeping a list of them is difficult. Some I know of are: QIC-157 (ATAPI tape), SFF-8070 (ATAPI Removable Rewritable Media), SFF-8080 (ATAPI CD-R/E) and SFF-8090 (Commands for DVD). Locating some of these documents can be difficult.


ATA/ATAPI-4 is ANSI document number INCITS 317-1998.

ATA/ATAPI-4 adds and changes many things. Here is a brief list:


ATA/ATAPI-5 is ANSI document number INCITS 340-2000.

ATA/ATAPI-5 deletes a few old commands, adds a few new commands, changes the way a few commands operate. But the big thing in ATA/ATAPI-5 are the two new and faster Ultra DMA 66 data transfer modes.


ATA/ATAPI-6 is ANSI INCITS project number 1410.

ATA/ATAPI-6 includes another even faster Ultra DMA mode 5, also known as Ultra DMA 100. It also includes a method of increasing the number of LBA bits from 28 to 48 and increasing the Sector Count from 8 bits to 16 bits.

Work on ATA/ATAPI-6 was completed at the T13 meeting in October 2001. ATA/ATAPI-6 should be a published ANSI standard in early 2002.

Serial ATA (SATA)

While T13 was working on ATA/ATAPI-6, a group of companies headed by Intel, was developing a serial version of the parallel ATA interface. READ ALL ABOUT SATA HERE!


ATA/ATAPI-7 is ANSI INCITS project number 1532.

Work on ATA/ATAPI-7 was completed in early 2005.

ATA/ATAPI-7 includes UltraDMA mode 6 also known as Ultra DMA 133, some new commands for use by digital video recorders, and the T13 version of Serial ATA (SATA). The ATA/ATAPI-7 document has been split into three volumes: one for the hard disk commands, one for the traditional parallel ATA interface and one for the SATA-1 interface. Unless you need documentation for a specific ATA/ATAPI-7 feature, avoid using ATA/ATAPI-7 - use ATA/ATAPI-6 or use ATA-8.



What Follows ATA-8 (It is not ATA-9)


Page updated 07 Apr 2008.