Replacing 8" drive with 3.5" drive on CP/M systems

From: Randy McLaughlin <>
Date: Fri Feb 11 20:16:40 2005

From: "Herb Johnson - null account" <>

Sent: Thursday, February 10, 2005 11:40 AM

<snip part about ignoring non-standard 3.5" drives>
<snip part about DD systems>
> Randy McLaughlin (general posts)
> ----------------
> Randy started the thread with his proposal for a "standard". In
> correpondence public and private, he has not quite appreciated the
> potential problems of single density (SD) and FM format unique to the
> oldest systems, versus the use of new HD drives and media. But I think
> he appreciates now there will be more than ONE "standard" which would
> include a SD scheme of some sort.
> My impression is that Randy has not considered that diskette drives and
> media are ANALOG devices. That is, the read write electronics, the drive
> head, and the media, have responses that depend on data rates
> (frequency) and modulation (FM and MFM). Consequently, they have have a
> marginal, unreliable response if they are used outside their design
> limits. That is, drives and media from different manufacturers can be
> DIFFERENT, and possibly inconsistent, in how they respond to any unusual
> (non-standard) schemes of data rates or formats. The worst of this is
> how HD drives respond to SD and DD formats and data rates from older
> systems. Also, response may change over time, as drives and media age.

The drives communicate with the computer via digital signal only. The
analog signals are generated on the drive itself. The signals being
generated by the CP/M 8" disk controllers match the signals generated by
modern PC's in all but one thing: Modern PC controllers use CMOS drivers.
Even this should not be an issue since they are TTL compatible.

I only intend to use the drives using the manufacturer specs the reliability
issue is simply the reliability of the drive/media alone.

<snip part dealing with 48TPI issues>
> HOWEVER some of the oldest diskettes like 8-inch do fail or perform
> poorly - why is not clear to me. And old 8-inch drives can just wear
> out, or fail and destroy media. It's a bad feeling when a disk drive
> head SCRAPES UP A DISK to bare plastic. So the issue of replacment and
> upgrade is a reasonable one.
> I'll note that I sell old floppy drives and media, and of course I have
> my own old systems, so I have my biases. That's why I try to find
> information and data, so others can become informed and draw their own
> conclusions, make their own decisions.

I do recommend using 8" drives and media, I have also just about cried when
I pull out a disk that was scraped.

When the drive scrapes the oxide off the diskette you must not use the drive
again until you clean all the oxide off the head(s), it will destroy every
diskette you stick into until it is cleaned! This issue happens most often
with Elephant brand diskettes but it can happen with any manufacturer, I had
a discussion about this Don Maslin.

> Herb Johnson
> --
> Herbert R. Johnson, voice 609-771-1503, New Jersey USA
> <a href=""> web site</a>
> <a href=""> domain mirror</a>
> **MY "" site & email is EXPIRED **
> my email address: herbjohnson ATT comcast DOTT net
> if no reply, wait & try: hjohnson AAT retrotechnology DOTT com
> "Herb's Stuff": old Mac, SGI, 8-inch floppy drives
> S-100 IMSAI Altair computers, docs, by "Dr. S-100"

3.5" drives are a viable media for CP/M systems, I am not telling people to
drop 8" drives. I hope people will come together and agree on one of the
"standards" published by the 3.5" drive manufacturers.

Further than that once a physical format can be agreed on then maybe we can
agree on a logical formatting scheme.

Received on Fri Feb 11 2005 - 20:16:40 GMT

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