An historical nit about FDDs

Tom Gardner t.gardner at
Thu Jul 12 13:02:25 CDT 2018

Hi Chuck

I agree it is easy to convert but I am surprised that a start-up would have the guts to change the "standard," whether it was Memorex, Potter or Century.  I think before the 33FD Memorex was the market leader but I could be wrong.  I've asked some SA founders the question.  Does anyone know any Potter or Century FDD people from the early 70s?

The early HDD interfaces I am aware of used a control cable with an 8-bit bus and a set of tag lines to define the bus - much more expensive to implement than the Step In/Step Out.



-----Original Message-----
From: Chuck Guzis [mailto:cclist at] 
Sent: Wednesday, July 11, 2018 11:38 AM
To: Tom Gardner via cctalk
Subject: Re: An historical nit about FDDs

On 07/11/2018 11:12 AM, Tom Gardner via cctalk wrote:
> Anyone know where the Step/Direction version of the FDD interface 
> originated.
> So far as near as I can tell the earliest FDDs (IBM 23FD Minnow and 
> Memorex
> 650/651) used Step In/Step Out. The IBM 33FD Igar used direct control 
> of the motor.
> The earliest Step/Direction FDD I can find is the Shugart 800 which 
> first shipped in September 1973.

Shugart is probably it, unless there's a hard drive interface that precedes it.  Mostly a minimal bit of logical difference between the Step in/Step out  and Step/Direction.  One can be converted to the other rather easily.


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