AT Attachment (I)

ATA AT Attachment

O hard disk que você chama de IDE, na realidade é um dispositivo de armazenamento do tipo ATA melhor dizendo PATA. O dispositivo ATA = AT Attachment, porque PATA? Porque este dispositivo é um dispositivo com interface do tipo paralela.

Os fragmentos de documentos que coloco baixo estão em inglês porque não há razão para tradução e são bem inteligíveis.

Parallel ATA (PATA), originally AT Attachment, is an interface standard for the connection of storage devices such as hard disks, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee. It uses the underlying AT Attachment (ATA) and AT Attachment Packet Interface (ATAPI) standards.

Gene Milligan, anyone using a data storage device owes much to Gene's efforts to develop and maintain the ANSI SCSI and ANSI ATA standard. Gene will be missed as chairman of ANSI NCITS T13 and even more so as a friend. Back in 1989 he was the editor of the original CAM ATA document, the first public document that described what we now call the ATA interface.

Gene Milligan died in November, 2000
ATA is the real name for the mass storage device interface that is frequently called IDE (Integrated Device Electronics) or EIDE (Enhanced Integrated Drive Electronics). IDE and EIDE are mostly used by marketing people who do not know what they are selling or by writers for magazines who do not know what they are writing about.

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 original ATAPI specification was called SFF-8020. The SFF-8020 specification is very old and very obsolete - do not use it - instead use the ATA/ATAPI-5 or -6 (avoid ATA/ATAPI-7) and the SCSI MMC-4 or -5 standards for the current description of ATAPI. The ATA-8 standard should be done later in 2008.

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.  
Wren was a very popular family of disk drives made by Imprimis. The well know OEM customer was Compaq Computer. ST506 (ST412) was the interface used by Seagate hard disk drives (MFM and RLL drives). Seagate has a long history of using the word disc instead of disk.

The first formal standard defining the AT Attachment interface was submitted to ANSI for approval in 1990. It took a looooooong time for this first ATA standard to be approved. :^) Presumably, it took so long because it was the first standard to define the interface, and therefore much debate and discussion probably took place during the approval process. It was finally published in 1994 as ANSI standard X3.221-1994, titled AT Attachment Interface for Disk Drives. This standard is sometimes called ATA-1 to distinguish it from its successors.

To start with Hard disks you can look for documents in two organizations, one is the T13 and the other is the T10, both have the docs about hard disks and its interfaces.

The first draft X3T10 DRAFT 791D Revision 4c 1994

Copyright 1994, Computer and Business Equipment Manufacturers Association. Permission is granted to members of X3, its technical committees, and their associated task groups to reproduce this document for the purposes of X3 standardization activities without further permission, provided this notice is included. All other rights are reserved.

When the first IBM PC (Personal Computer)(tm) was introduced, there was no hard disk capability for storage. Successive generations of product resulted in the inclusion of a hard disk as the primary storage device. When the PC AT (tm) was developed, a hard disk was the key to system performance, and the controller interface became a de facto industry interface for the inclusion of hard disks in PC ATs.

The price of desktop systems has declined rapidly because of the degree of integration to reduce the number of components and interconnects required to build a product. A natural outgrowth of this integration was the inclusion of controller functionality into the hard disk.

In October 1988 a number of peripheral suppliers formed the Common Access Method Committee to encourage an industry-wide effort to adopt a common software interface to dispatch input/output requests to SCSI peripherals.

Although this was the primary objective, a secondary goal was to specify what is known as the AT Attachment interface.

T13 is a Technical Committee for the InterNational Committee on Information Technology Standards (INCITS). INCITS is accredited by, and operates under rules approved by, the American National Standards Institute (ANSI). These rules are designed to ensure that voluntary standards are developed by the consensus of directly and materially affected interests. INCITS develops Information Processing System standards, while ANSI approves the process under which they are developed and publishes them. The INCITS web site may be accessed at http://www.incits.org/. Of particular interest is the INCITS Antitrust Policy.

T10 is a Technical Committee of the InterNational Committee on Information Technology Standards (INCITS, pronounced "insights"). INCITS is accredited by, and operates under rules that are approved by, theAmerican National Standards Institute (ANSI). These rules are designed to insure that voluntary standards are developed by the consensus of industry groups. INCITS develops Information Processing System standards, while ANSI approves the process under which they are developed and publishes them. ANSI also serves as the representative for the United States on Joint Technical Committee - 1 (JTC-1) of the International Standards Organization (ISO) and the International Electrotechnical Commission (IEC).

Collect these fragments of documents in 1999 to start a small course about hard disk