Please see embedded comments below.
Dick
----- Original Message -----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, March 27, 2000 12:38 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
>
> Are you trying to say that the coercivity of the disk (which is a
> physical property of said disk) will somehow magically change when you
> try to write a 360K format to it? If not, what are you saying?
>
> > considering that toward the "maturity" of the 5.25" technology, the
media
> > available throughtout the market were really pretty much the same, and
the
>
> Right up until the end, reputable disk manuafacturers put different media
> into 360K and 1.2M disks. Period.
>
> > drives were pretty similar too, except for the differences essential to
> > maintaining their functionality. After the "new" had worn off the
1.2MB
>
> These 'differences' included things like the coercivity of the disks and
> the head width in the drives.
>
> > Each step of the way created confusion in the market. Eventually the
> > technology was abaondoned for the superior 3.5" drives. Nevertheless,
the
>
> Actually, there's a nasty design defect in 3.5" disks. The side of the
> shutter nearest the spindle is not clamped together in any way, and can
> spring apart. This produces a disk that will slip into a drive OK but
> which won't come out again (think of a standard locking barb). To get it
> out involves dismantling the drive. I've had to sort this little mess out
> a few times...
>
> > 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.
>
> Oh, OK. If you're using a genuine 360K disk, then there is, indeed, no
> problem with the disk (because it's the right one to use). But somebody
> was claiming you could format a '1.2M' disk in a 1.2Mdrive with a 360K
> format and then expect it to be reliably read by a 360K drive. That, in
> my experience, doesn't work. Most of the time it won't even format
> properly (the 1.2Mbyte drive being set to use a lower write current as I
> mentioned a couple of messages back).
>
That was my point. The way this thread got to this topic was that someone
was trying to write a 360 KB diskette witha 1.2MB drive and expected an old
Commodore (?) to read it. While it's quite possible, I doubt one would
call it likely.
> >
> > > 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.
>
> Agreed! These people are fools. Period.
>
> My data is worth a lot more than the cost of _any_ floppy disk you care
> to name. It is _always_ worth using the best disks available (which means
> also using the _correct_ disk ).
>
> >
> > > 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
>
> Actually, it was the same software (be it part of the bios or a separate
> driver) that was used with 720K 3.5" disks.
>
> > loaded. I once made the hole in a few 720K diskettes because I needed
the
> ^^^^^^^^^^^^^^
> Presumably you're now talking about 3.5" disks.
>
Yes. I was disappointed with the results, however.
>
> > 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,
>
> Every 3.5" drive I have ever worked on uses mechanical sensors for write
> protect, high density detect, and disk inserted. I have never seen
> optical sensors, not even on the old Sony units [1]. In any case the
> mechanical sensor is nearly always a thin 'pin' that goes through the
> middle of the hole. It certainly doesn't check that it's a square hole.
>
> [1] These being the full-height 600rpm units.... These drives did use
> optical sensors -- slotted optoswitches on the spindle motor PCB. But
> they were operated by spring-loaded plastic pieces that carried 'pins'
> that went through the holes in the disk. So the actual interface between
> the disk and the sensors was still a mechanical pin.
>
> -tony
>
Received on Mon Mar 27 2000 - 16:09:40 BST