Allison ajp166 at
Thu Nov 27 14:37:52 CST 2008

>Subject: Re: IDE <-> MFM
>   From: ard at (Tony Duell)
>   Date: Thu, 27 Nov 2008 19:35:41 +0000 (GMT)
>     To: cctalk at
>> On Wed, 26 Nov 2008, Jules Richardson wrote:
>> > Fred Cisin wrote:
>> >> IIRC, my Compaq "Portable 286" (NOT the "Portable 2")
>> >> had a pre-standardization ISA IDE "controller" that cabled to a bridge
>> >> board on an MFM drive
>> >
>> > Isn't that the other way around, though: IDE controller -> bridge -> MFM 
>> > drive?  The previous poster's saying* they're doing this the other way
>> That doesn't make sense. IDE stands for Integrated Drive Electronics, 
>> which means that the controller is located on the drive. Therefore IDE 
>> controller cards don't exist, and you can't bride IDE to an ST-412 
>OK, but IDE bus interface cards do exist. Meaning cards that link ISA 
>(or whatever) bus to an IDE drive. For ISA, it's little more than an 
>address decoder and buffers (I happen to be using one in this PC). 
>> interface type drive.
>Sure you can. Make a PCB containing a WD1003-like disk controller. On one 
>side, have ST412 connectors to conencto to that sort of drive. On the 
>other, have an IDE interface -- data lines, 3 address lines, etc. In 
>other words the original PC/AT disk controller board minus the floppy 
>controller and minus most of the address decoder. Linked to the IDE bus 
>interface I mentioned just now, you have a complete ST412 hard disk 
>controller system. And the seond part of it could reasonably be called an 
>IDE (host interface) to ST412 (drive interface) bridge board.

If I needed to go from IDE to MFM I'd go to my junk box and pull out a 
WD1003 (or one of the smaller versions) and fake the interface of 
IDE to ISA16.  The two are so close its only the matter of the 
IO address lines to resolve them down to CS1 and CS2.  Command wise 
the 1003 was the prototype for IDE command set.


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