Cromemco 4FDC, How do you format a disk?

From: Fred Cisin <>
Date: Wed Jul 28 19:43:31 1999

> I nearly did. It was just that I couldn't find a spare 3.5" drive when I
> had the M4 in bits. One day I'll come across one. I don't use 3.5" disks
> much, apart from on the PCs. The other machines have 'real' disk drives :-)
> I am also a great believer in making measurements rather than just trying
> it (which seems, alas, to be the modern thing to do). What if it works. I
> don't know if the pulse rate really is similar, or if I was just lucky
> and the drive could handle a strange data rate. By making the
> measurement, I know what is going on.

My understanding back when the 720K 3.5 was being develeoped was that it
was INTENDED to be fully interchangeable with the 5.25". Therefore, it
"should" be OK, if the design spec for full interchange was adhered to..
BUT, there's always the possibility that "because NOBODY EVER uses FM
anymore,..." that they could have cut some corners that might interfere
with something that is still nominally part of the spec. That, of course,
could differ from one brand of drive to another.

> I believe the 3.5" drive will work as well. That's what this discussion
> is about. If it doesn't, I will have to investigate why not, since all
> the measurements I've made so far say that it will.

> > But then there are the INTERESTING ones:
> Most PC controllers keep the drive turning at 360rpm and use the 300kbps
> data rate.
MOST. I was surprised the first time that I encountered the dual speed.

> > Weltec 1.2 XT: To handle 1.2M diskettes in PC/XT, which only supported a
> > 250K data transfer rate, Weltec made a 1.2M drive that ran at 150 RPM!
> 150rpm? Surely it should be 180rpm (== half the 360rpm of a normal 1.2M
> disk with the 500kbps data rate).
That's right. 180RPM. Sorry.
> That's one I've never seen....
I don't think that it was around for long.

Other oddballs:
Tandon TM100-4M: 100TPI, instead of 96. I think that the M may have
stood for "Micropolis", who were the early 100TPI.

3": common in some circles

3.25": Dysan bet the company on soft-sided floppies. Has anyone ever
seen one in anything other than a Seequa Chameleon 325? Anyone ever seen
the 325? Anyone need some used blank floppies? I might even still have
an alignment disk or 2.

67.5TPI (40 track) 3.5": used for the Epson Geneva PX-8

Anyone know what the RS M100 "Portable disk drive" FIRST model used? Was
it FM?

2.8 M Barrium Ferrite:




Amlyn: weirdest drive that I've got. Somewhat deeper than usual full
height 5.25, sticking out quite a bit. Used a holder holding 5 600
Oerstedt diskettes, with disk changing under software control, for a total
of 6M. Was marketed for PC/XT, so it had it's own controller. Supposedly
used analog positioning, and could handle 48, 96 and 100 TPI! I'll
believe that if/when I can finally get around to checking it out.

Fred Cisin            
Received on Wed Jul 28 1999 - 19:43:31 BST

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