Using 3.5" HD drives on CP/M systems

From: Randy McLaughlin <>
Date: Sun Feb 6 13:30:50 2005

From: "Vintage Computer Festival" <>
Sent: Sunday, February 06, 2005 12:21 PM
> Here's a suggestion...
> The Epson PX-8 had 3.5" drives available as an add-on. The PX-8 was of
> course a CP/M machine. Why don't you start by investigating what Epson
> did?
> Sellam Ismail Vintage Computer
> Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger
> [ Old computing resources for business || Buy/Sell/Trade Vintage
> mputers ]
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> ]

This is an example of missing the primary assumption:

The 3.5" drives used on most CP/M systems are driven at 250K MFM.

3.5" DD (125K FM, 250K MFM) are simple extensions of 5.25" 48tpi drives.

I am concerned about 3.5" HD (250K FM, 500K MFM). This environment has the
same transfer rate as standard 8" drives but it uses a different rotational
speed. This means that you can not simply extend an existing format.

One other point that keeps coming up is using 3.5" DD exclusively. Many
systems can not handle this data rate other systems would require hardware
modifications, another point is the storage would be 1/2 of HD.

For systems running 250K FM (8" single density) would normally use 26
sectors at 360 RPM, 32 sectors at 300RPM. This is the issue, given that new
formats are required. The question is can enough people agree what formats
are appropriate?

To me 250K FM would obviously be best to use 32 128 byte sectors even though
going by Teacs FD235HF manual you can use 18 256 byte sectors or 10 512 byte
sectors. This is the closest to the 8" SSSD standard available.

Received on Sun Feb 06 2005 - 13:30:50 GMT

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