Reading ESDI disks

Jon Elson elson at
Thu Feb 11 12:22:29 CST 2021

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.


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