Whence IDENTIFY DRIVE?

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2021-06-12 05:30:03

As most everyone knows, the AT Attachment standard (informally known as IDE) started by literally bolting the previously standalone AT disk controller onto a MFM drive with a ST506 interface and connecting the assembly to the host system with a 40-pin ribbon cable.

As it often happens, the standardization process was far behind the technology and the first ATA standard officially became ANSI standard X3.221-1994 in (obviously) 1994. The standard had been in the works for several years by that time, but even so the first ATA standard drafts appeared in mid-1990, when at least half a dozen vendors have been shipping ATA drives for some time.

From a software perspective, an IDE drive is almost indistinguishable from an ST506 drive plus an AT controller—in fact that was the whole point of IDE. One crucial difference is the IDENTIFY DRIVE command.

The IDENTIFY DRIVE command (soon renamed to IDENTIFY DEVICE, in order to reflect the broadened scope of ATA) makes it possible to build self-configuring systems, also known as Plug and Play, even though apparently no one thought of calling it ATA PnP until about 1995. But where did it come from and why?