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.
The original IDE/ATA standard defines the following features and transfer modes:
- Two Hard Disks: The specification calls for a single channel in a PC, shared by
two devices that are configured as master and slave.
- PIO Modes: ATA includes support for PIO modes 0, 1
and 2.
- DMA Modes: ATA includes support for single word DMA
modes 0, 1 and 2, and multiword DMA mode 0.
"Plain" ATA does not include support for enhancements such as ATAPI support for non-hard-disk IDE/ATA devices, block mode
transfers, logical block addressing, Ultra DMA modes or other advanced features. Drives
developed to meet this standard are no longer made, as the standard is old and obsolete.
In fact, at the recommendation of the T13 Technical Committee, ATA-1 was withdrawn
as an official ANSI standard in 1999. This is presumably due to its age, and the large
number of replacement ATA standards already published by that time.
Next: ATA-2
