Five and quarter drives

[Eric Smith]

Randy wrote:
> When the PC-AT first came out there were two different types of 1.2M
> drives:
>
> 360RPM using 600K transfer rate & 300RPM using 500K transfer rate.

Neither of those were used by the AT, and they would not be compatible
with the AT HD disk format.

> Gets confusing doesn't it?

Yes.

The AT used 500 Kbps at 360 RPM for HD mode.  If IBM had used
300 RPM for high-density drives (which they didn't), they would
have had to use 416 Kbps to get the same on-disk format.

Eric