Using 3.5" HD drives on CP/M systems

From: Randy McLaughlin <>
Date: Fri Feb 4 17:37:28 2005

From: "Herb Johnson" <>
Sent: Tuesday, February 01, 2005 1:10 PM
> "Randy McLaughlin" writes [in exerpts,, my text in brackets]:
> I think Randy is looking for a CONSENSUS, not a "quorum", but in any
> event he is looking for an acceptable standard. He did not get a lot of
> responses because 1) it's only been a few days, and 2) it's a
> technically tough subject, and 3) it's an OLD subject over the years.

In fact I am hoping to put togather a quorum, I want a select group of
technically minded people to come together and have their own opinions and
ideas. CP/M on 3.5" drives exist. 3.5" HD media has technical issues that
are unique to it.

If we can get a quorum then a consensus can be formed.

> Randy suggested in his comp.os.cpm posts that it's basically OK to write
> in single density FM format on 3.5" high-density (HD) media, as he says
> the "flux changes in FM and MFM" are at the same rate. For the oldest
> computers, FM is the ONLY format option you may have. I did not respond
> to Randy's post. But I think the problem of that scheme for use at 3.5"
> HD will be two-fold. First, the actual data rates of old single density
> FM 8-inch FDC's are much slower than standard data rates for HD 3.5"
> media; the same applies for the read/write electronics of the DRIVE.
> Second, no "modern" computer which uses 3.5" 1.4M drives is likely
> CAPABLE of reading an FM encoded (single density) data stream, except by
> accident. This calls to mind a classic problem on IBM compatibles,
> namely reading old 5.25" 360K SINGLE density diskettes (like Osborne
> diskettes). The FDC chip and/or decoder does not "expect" an FM encoded
> data stream.
> Frankly, I find this kind of discussion VERY CONFUSING, as there are a
> number of design specifications in play. Note all the technical issues
> above: media, data rates, read/write electronics - not to mention how
> drives are switched, or switch "themselves" between these various
> schemes. As such discussions have occured many times before in
> comp.os.cpm, I decided to compile the best posts and primary-source
> technical data on my own Web site, and to refer others to it when
> appropriate. (My site draws no conclusions, it just posts specs, code,
> and other's technical discussions.)

I posted extracts of information about FM on HD systems from some great
information posted on Herb's site. Actually it is a link to the specs of
Teac's FD235 drive. It has a table of recomended physical formatting
schemes and FM is included.

I agree that finding a PC that can handle FM is basically impossible for a
new off the shelf system, which is why I keep an old PC that does handle FM.

In this case it does not matter what drive and media is used if all you have
is FM then 3.5" FM is accepatble While you won't be able to use it on most
PC's that applies for any FM disk (3.5", 5.25", or 8"). Note I am not
recomending anyone stop using 8" I just am recomending standardizing how we
use 3.5" when we do use it.

> In my opinion, the "point person" on issues of disk and drive is
> Amardeep S Chana. He has posted for years on that subject and his
> technical knowledge and experience are apparent in his many posts.
> Bruce Jones has "walked the walk" and written code and documents how it
> works, which he shares freely and which others have put to use. Both
> have content on my site, with their permission, via the links above.
> One personal note. This took a few hours to write. It takes time to make
> a good, technical "argument". It took time for me to complile all the
> info on my site, and time for THOSE people who wrote it to do their
> work. It does not take long to propose a popular idea, and it's fun;
> it's less popular (and more work) to say "here's why it may not happen".
> Herb Johnson

I appreciate your comments, I agree that no standard is in site and may
never be agreed upon by enough people. I also agree we need Amardeep and
other to pipe in.

I expect a large base to fight using 3.5" media but I find that 3.5" media
is so much easier to deal with on a variety of levels.

> ------------------------------
> 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
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Received on Fri Feb 04 2005 - 17:37:28 GMT

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