360K in a 1.2M drive (was: Parallel port hard drives?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Mar 27 00:24:14 2000

I'm in agreement, pretty much with what's been said here. Please see
embedded comments below.

Dick

----- Original Message -----
From: Fred Cisin (XenoSoft) <cisin_at_xenosoft.com>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, March 26, 2000 8:12 PM
Subject: Re: 360K in a 1.2M drive (was: Parallel port hard drives?


> There are TWO problems.
>
> The disk matters.
> The drive matters.
>
> 360K is 300 Oerstedt. 1.2M is 600 Oerstedt.

Yes, but, given that the goal is to write a 48TPI 360K diskette, the
coercivity will be the same, since the media are the same. It's worth
considering that toward the "maturity" of the 5.25" technology, the media
available throughtout the market were really pretty much the same, and the
drives were pretty similar too, except for the differences essential to
maintaining their functionality. After the "new" had worn off the 1.2MB
technology, drive makers started migrating the new technology onto the
"standard" line of products because they could sell more. Once production
was in full swing it was a better practice to put the same electronics and
heads onto all their drives instead of maintaining various technologies.
Each step of the way created confusion in the market. Eventually the
technology was abaondoned for the superior 3.5" drives. Nevertheless, the
media need not be considered for purposes of THIS discussion because the
target medium is the 300-Oerstedt 48TPI 5.25" diskette. The issue was that
the old 48TPI disk drive had trouble reading the 48TPI diskette written on a
1.2MB 96TPI drive. The reason is not the media, it's the drive. Why?
It's because the medium is the same physical diskette. It cancels out of
the equation.

> Using the wrong coercivity of diskette, you will NEVER get a good,
> reliable result. You MIGHT sometimes almost get away with using the
> worng diskette. SOME idiots will claim that they "always use the wrong
> diskette". WHY???

There are folks who enjoy claiming that their risky way of doing things is
better than paying the 10% extra for the correct product.

> BTW, 720K and 1.4M are nominally 600 Oerstedt and 750 Oerstedt, which is
> close enough that "getting away with" is a MUCH more likely proposition.
>
Let's try to keep the 3.5" diskettes out of the picture for now. The 720K
diskettes I meant were the 80-track 5.25" drives of the pre-PC/AT days.
These were quite popular in the late '70's-early '80's, and were
occasionally used with PC's, though they required a special driver be
loaded. I once made the hole in a few 720K diskettes because I needed the
media and felt I could get by. It worked, but it wasn't long before the
optical sensors in the early 3-1/2" drives gave way to the mechanical
feelers, and the holes had to be square. That wasn't very convenient, and,
by the way,
>
> There are several problems with using the wrong drive. But some times
> there isn't an adequate alternative.
>
> Read/write currrent level:
> With the exception of some of the preproduction Mitsubishi 4854 and
> prototype Shugart 475s, all of the 1.2M drives have explicit provision for
> TWO read/write current levels, explicitly for the purpose of permitting
> reading, and even writing, 360K diskettes in the 1.2M drives. That is
> typically NOT where the problem arises.
>
> Motor speed:
> 8" is at 360RPM; 1.2M is at 360RPM 360K is at 300RPM
> To do 360K in a 1.2M drive typically requires that the controller

Some of the controllers switched the data rate and in other cases the drive
switched speed.

> compensate for the different motor speed by running the 360K data transfer
> rate at 300Kbps instead of the usual 250K bps. PC controllers can
> normally handle that. Hooking a 1.2M drive to a non-PC controller that
> expects an 8" drive will not provide for that, and therefore will not work
> right for trying to do 360K diskettes.
> Many current drives have dual spindle speeds (300, 360)
> Weltec once made a 180RPM drive that would permit a PC 360K controller to
> do 1.2M diskettes! (reliability was less than ideal)
> THAT is typically not where the problem lies.
>
> Track width:
> Track width is a problem. Not only with 1.2m drives and 360K diskettes,
> but also even with 720K/800K 5.25" drives (Shugart 465, Tandon TM100-4,
> etc.) with 360K disk formats.
> 360K is about 1/2 mm per track, and the actual track itself is about 1/3mm
> wide.
> 1.2M, 720K 5.25", etc. is about 1/4mm per track, and the actual track
> itself is about 1/6mm wide.
>
> When working with a virgin, bulk-erased 300 Oerstedt diskette, the 1.2m
> (or 720K 5.25") drive CAN produce a diskette using every other track, that
> is ALMOST acceptable. It will have tracks that are only 1/6mm wide, but
> properly spaced at 1/2mm increments. You normally CAN get away with that,
> unless/until:
> if you EVER write to THAT diskette with a 360K drive, even "just erasing a
> file", you will have replaced that 1/6mm wide sector with a 1/3mm wide
> sector. From that point on, the diskette should NOT ever be written to
> with the 1.2m drive, unless/until it has been bulk-erased and formatted
> again.
>
> A 96TPI drive can NOT do an acceptable job of REformatting or REwriting
> over a 1/3mm wide track! Some people, using SOME drives have found that
> it is ALMOST good enough, and can sometimes get away with it. But that's
> like trying to use MY car at 100 mph. It just isn't built to do it RIGHT.
>
> Therefore, it IS possible to do an emergency transfer diskette from 1.2M
> to 360K, using a 300 Oerstedt diskette. But repeated back and forth
> requires careful attention to detail to avoid ever trying to rewrite a
> 1/3mm wide track with the 1.2M drive.
>
> --
> Grumpy Ol' Fred cisin_at_xenosoft.com
>
Received on Mon Mar 27 2000 - 00:24:14 BST

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