ATA Standards At A Glance
In the following paragraphs, we'll discuss the individual evolutionary stages of ATA. The summary table at the end will provide you with the details.
ATA-1
This is the mother of all IDE standards, from 1994. This specification provides one channel with which two drives can be run (master and slave). It supports PIO modes 0, 1 and 2 (Programmed I/0), as well as DMA modes 0, 1, 2 (Direct Memory Access) and Multiword-DMA 0. Because of its age, ATA-1 is unable to handle CD-ROM drives, as these are based on ATAPI (starting with ATA-4). Nor does it support the performance-boosting block mode or logical block addressing - with the result that the maximum usable hard drive capacity is limited to 528 MB.
ATA-2
Things just weren't moving fast enough for hard drive manufacturers, which is why Seagate (Fast-ATA) and Western Digital (Enhanced IDE) decided to take matters into their own hands. By 1996, ANSI had managed to adopt ATA-2 as an "ATA interface with extensions" that included the following improvements:
PIO modes 3 and 4 were added, as were Multiword DMA modes 1 and 2. Furthermore, ATA-2 also supported block transfers and addressing hard drives using Logical Block Addressing (LBA). Various enhancements for simple identification of the drives were integrated as well, enabling BIOS to independently detect the hard drive and all its drive parameters for the first time.
What was left were the different terms coined by the marketing departments.
ATA-3
This standard was published as X3.298-1997 in 1997, and offered relatively few improvements. These mostly involved the reliability of the fast transfer modes (Multiword DMA 2 and PIO 4) because conventional 40-wire IDE cables often presented a source of errors. For the first time, a feature for actively improving reliability was introduced: since 1998, SMART (Self-Monitoring Analysis And Reporting Technology) has been prompting hard drives to check themselves and then report errors to BIOS.
The standard itself has been officially adapted only rarely due to the lack of faster transfer modes. Instead, many manufacturers decided to use such features as SMART without actually complying with ATA-3 specifications. That's why compatibility issues continued to arise.
