Reading ESDI disks

[Fred Cisin]

On Thu, 11 Feb 2021, 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.
> What am I missing?

I'm more than a LITTLE confused by parts of this discussion.

To what extent are ESDI controllers interchangeable with already written 
drives?
Remember that XT/5160 ST506/412 controllers were often NOT 
interchangeable, although AT/5170 ones usually were.
Mattis says that he has the controller that that drive was written with.


Some folks are talking about how the controller talks to the drive. If 
using OS or BIOS (mine had a ROM), unless changing THAT, such as trying to 
use a flux-transition device, controller to drive communication seems 
largely irrelevant.

At least in the case of ISA, for the sake of compatibility, and 
transition, the controller and drive COMBINATION looks the same to the 
computer/OS as an ST506/412.

Similarly, on PCs, IDE typically, for the sake of compatibility, and 
transition, the controller and drive COMBINATION looks the same to the 
computer/OS as an ST506/412.

Similarly, on PCs, ATA typically, for the sake of compatibility, and 
transition, the controller and drive COMBINATION looks the same to the 
computer/OS as an ST506/412.

All followed the ST506/412, and strived for transparent compatibility, 
but did not necessarily derive from each other.