After some digging, I discovered that several old drafts of the original ATA standard (later known as ATA-1) have been out in the public all along, or at least for a very long time, cleverly hiding among hundreds of SCSI-related documents. I don’t seem to be the only one who missed them. Here they are:
- DAD (Disk ATBus Definition) Rev 1, March 30, 1989. Very incomplete.
- ATA (AT Attachment) Rev 2.1, June 11, 1990.
- ATA (AT Attachment) Rev 2.2, August 15, 1990. Last under the CAM heading.
- ATA (AT Attachment) Rev 2.3, January 30, 1991. Under the new X3T9.2 heading.
- ATA (AT Attachment) Rev 3.0, November 22, 1991.
- ATA (AT Attachment) Rev 3.2, October 16, 1992.
- AT Attachment Interface for Disk Drives, January 3, 1993, ANSI X3.221. Official ISO/IEC/ANSI draft. Probably revision 3.3A.
- AT Attachment Interface for Disk Drives, March 17, 1993, Revision 4.
These old revisions may provide the best surviving documentation of existing ATA/IDE practice as it existed in 1989 and onward. The first working document was introduced in March 1989. The ANSI X3.221 standard was officially approved on May 12, 1994. The actual document text was finalized in late 1993.
Note that the 1991 drafts still did not include any LBA support or removable media support. It did include the IDENTIFY DRIVE command as well as the (optional) READ/WRITE MULTIPLE and SET MULTIPLE MODE commands, as well as slave DMA transfers and PIO modes 0, 1, and 2 (up to 8.33 MB/s interface transfer rate).
July 2020 Update: Two “new” ATA draft versions have been discovered in BBS archives, namely revisions 3.0 and 4. While the R3.0 document was a plain ASCII file, the R4 file was not and used IBM code page 437 extended characters. The file presented above was converted to UTF-8; the original R4 document is here. As the notes in R3.2 indicate, R3.0 from late 1991 did not yet have any concept of LBA.
October 2021 Update: Two more and even older ATA drafts came to light. The very first and very incomplete draft (not yet called ATA) from March 1989, and a much more complete revision 2.1. The R2.1 draft is quite recognizable as ATA. The document was converted from WordStar to PDF, using the same 2-up printing style that X3T9.2 used for draft standards back in the day. The original R2.1 draft is here.