27 Dec
2003
27 Dec
'03
7:12 a.m.
Good explain !
You could consider to put in like a FAQ ;-)
(not a joke).
But more seriously, I shall check this with one of the old diskettes.
Thanks and Greetings
Sergio
----- Original Message -----
From: "Fred Cisin" <cisin(a)xenosoft.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk(a)classiccmp.org>
Sent: Saturday, December 27, 2003 9:19 PM
Subject: 720K v 1.4M (NOT: PC 160K and 320K are NOT SINGLE DENSITY
On Sat, 27 Dec 2003, SP wrote:
This matter make me think in the problem with the
1.44 Mb floppies
we have from 1993 to this date. In that time you could purchase 720k
floppies and format it like 1.44Mb floppies without problem. And, even
more important, read one 720K floppie formated like one of 1.44Mb.
This was valid until the IBM PS VP. This was the last. If I remember
it correctly, all the models of floppies of PCs' began to fail in the
management of this floppies on this date. Bad matter, because I already
have a lot of them with BBS stuff and Clipper libraries from these years
that I can access only with one IBM PS/2 70 that I have in the garage.
YOUR problem can be easily repaired with a hole punch and some
opaque tape.
What you are describing sounds like an issue of the MEDIA SENSOR.
The original PS/2 drives did not have a sensor. They could not
tell the difference between a 720K 3.5" and a 1.4M. If you put
a virgin BLANK diskinto the drive, it would assume 1.4M and
format it as such, disunirregardless of which kind of disk it
really was. It would then work marginally OK as that.
Or, you could put a virgin blank 1.4M diskette into the drive,
and LIE about what it was ("FORMAT A: /T:80/N:9"), and it would
become a marginally usable 720K diskette.
720K diskettes were 600 Oersted, and 1.4M were about 720
to 750 Oersted, so you could take a good 720K diskette and
turn it into a mediocre 1.4M, or take a good 1.4M diskette
and make it into a mediocre 720K.
THAT is why they will work with your PS/2 model 70.
When other companies got into 1.4M drives, they included a
"Media Sensor" which could tell which kind of diskette was
in the drive, by looking for that other hole that is
symmetrical to the write protect.
But when you put one of your WRONG diskettes into one of
those drives, it is sensing what kind of diskette it REALLY
is, instead of what you are using it as.
THAT is why they will not work with anything other than your PS/2.
Take one of your 1.4M diskettes that you have been using
as a 720K; put opaque tape over the media ID hole; and
try it again.
Take one of the 720K diskettes that you have been using as
a 1.4M, and punch a hole through it, and try it again.
Back when 1.4M diskettes cost more than 720K, there were
commercially available punches sold to suckers and
cheapskates. Those punches weren't needed for cheapskates using PS/2s.
Modern machines WILL still handle 720K.
Even Windoze XP WILL still handle 720K!
But the FORMAT options are no longer documented.
/F:2 no longer works.
/F:720 no longer works.
but, /T:80/N:9 DOES still work!
[Confirmed on current Compaq machines. YMMV]
--
Grumpy Ol' Fred cisin(a)xenosoft.com