27 Mar
2000
27 Mar
'00
8:09 a.m.
Please see embedded comments below.
Dick
----- Original Message -----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, March 27, 2000 12:38 PM
Subject: Re: 360K in a 1.2M drive (was: Parallel port hard drives?
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
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.
is
the
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 > 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).
>
> > 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 > > 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
^^^^^^^^^^^^^^
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