Reading ESDI disks

[Jon Elson]

On 02/11/2021 11:36 AM, Chuck Guzis via cctalk wrote:
>
> I'm a little confused on this.  An ESDI drive, in my experience, behaves
> exactly like an ATA one, right down to the command set.   ESDI drives
> can be soft-or-hard sectored.
>
>
No.  ESDI is similar to MFM, there is a differential read 
data pair on the 20-pin connector, but the data rate is much 
higher, 10, 15 or 20 MBit/sec, and used a different encoding 
scheme that gave more data bits/flux transition.  I think 
the 34-pin connector also allowed an additional head select bit,
so you could have up to 16 heads.

ATA has a single 40-pin connector with a 16-bit parallel 
data bus for all command and data transfers.

Jon