22 Mar
2010
22 Mar
'10
8:37 p.m.
On 22/03/2010 19:18, Alex Taylor wrote:
The idea was that reformatting a 1.44MB HD disk in a
DD drive will
leave traces of the original formatting behind (as they're always
preformatted for DOS/Windows), causing the unreliability. Using a bulk
eraser is meant to eliminate this problem, as it will turn them into
completely blank disks that can be formatted in a DD drive more
reliably.
That won't really matter. When you format a disk you write bit patterns
all over it: in the headers, in the data sectors, and even in much of
the gaps between them (sync bytes and clock patterns used as markers).
Thus there's something there even when you write the first real data,
and of course it never lines up exactly, bit for bit. Therefore you
still have the problem of interference from the previous "data" even if
it's just the dummy data used to fill a "blank" sector, and the sync
bytes and markers in the preamble to it.
--
Pete Peter Turnbull
Network Manager
University of York
22 Mar
22 Mar
8:54 p.m.
On 22/03/2010 19:18, Alex Taylor wrote:
The idea was that reformatting a 1.44MB HD disk in a
DD drive will
leave traces of the original formatting behind (as they're always
preformatted for DOS/Windows), causing the unreliability. Using a bulk
eraser is meant to eliminate this problem, as it will turn them into
completely blank disks that can be formatted in a DD drive more
reliably.
In addition to all that, . . .
The coercivity (sorta like magnetic sensitivity) is WRONG.
"720K" diskettes are 600 Oersted.
"1.4M" diskettes are about 750 Oersted.
It IS close (unlike 360K (300 Oersted) v 1.2M (600 Oersted)), and it WILL
work (unlike 360K v 1.2M), but it will NOT be as reliable as using the
correct diskette.
9:10 p.m.
Fred Cisin wrote:
In addition to all that, . . .
The coercivity (sorta like magnetic sensitivity) is WRONG.
"720K" diskettes are 600 Oersted.
"1.4M" diskettes are about 750 Oersted.
It IS close (unlike 360K (300 Oersted) v 1.2M (600 Oersted)), and it WILL
work (unlike 360K v 1.2M), but it will NOT be as reliable as using the
correct diskette.
It would need to be for those punchout devices that where sold back in
the early 90s to 'convert' 720K disks to 1.44MB disks by punching the
detect hole out.
Mind in my previous job I had to take a drill to a 720K disk that a
studenet had formatted as a 1.44MB disk on his Archemedes, oddly the PC
could not read it. Once the hole was drilled it worked fine.
Was this just one model of Archemedes that had this 'feature' or was it
Acorn deciding that they could ignore the standard ?
Cheers,
Phill.
--
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
"You can twist perceptions, but reality won't budge" -- Rush.
9:15 p.m.
On 3/22/2010 8:10 PM, Phill Harvey-Smith wrote:
It would need to be for those punchout devices that
where sold back in
the early 90s to 'convert' 720K disks to 1.44MB disks by punching the
detect hole out.
I have one sitting right here as a testament to digital flim-flam men.
It's solid steel. I remember the advertising: "We formatted, read, and
wrote this disk 30 DAYS IN A ROW without a single error!" Yes, well,
try to read that disk six months from now and you'll find the contents
completely faded.
Was this just one model of Archemedes that had this
'feature' or was it
Acorn deciding that they could ignore the standard ?
All PS/2 Model 30-286 machines had this quirk too (completely ignored
the detect hole and always assumed 1.44MB media). I could never figure
out why I couldn't read my friend's 720K disks until I burned a hole
into it using a soldering iron on a hunch.
I continued that practice into college because I was a broke college
student. After losing part of an assignment due to bit fade, I started
taping the holes back up...
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
9:26 p.m.
> It would need to be for those punchout devices
that where sold back in
> the early 90s to 'convert' 720K disks to 1.44MB disks by punching the
> detect hole out.
On Mon, 22 Mar 2010, Jim Leonard wrote:
I have one sitting right here as a testament to
digital flim-flam men.
It's solid steel. I remember the advertising: "We formatted, read, and
wrote this disk 30 DAYS IN A ROW without a single error!" Yes, well,
try to read that disk six months from now and you'll find the contents
completely faded.
One of them had an advertisement where they stated that they had carefully
compared the two types of dikettes with a MICROMETER, and determined that
they were the same.
10:01 p.m.
Fred Cisin wrote:
One of them had an advertisement where they stated
that they had carefully
compared the two types of dikettes with a MICROMETER, and determined that
they were the same.
It's rather Ironic really that we started this discussion because we
wanted to do the reverse of what these punches did......
Cheers.
Phill.
--
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
"You can twist perceptions, but reality won't budge" -- Rush.
9:21 p.m.
On Tue, 23 Mar 2010, Phill Harvey-Smith wrote:
Mind in my previous job I had to take a drill to a
720K disk that a
studenet had formatted as a 1.44MB disk on his Archemedes, oddly the PC
could not read it. Once the hole was drilled it worked fine.
Was this just one model of Archemedes that had this 'feature' or was it
Acorn deciding that they could ignore the standard ?
It wasn't ONLY Acorn.
Most of the early PS/2 3.5" drives had no media sensor.
10:05 p.m.
On 22 Mar 2010 at 17:54, Fred Cisin wrote:
In addition to all that, . . .
The coercivity (sorta like magnetic sensitivity) is WRONG.
"720K" diskettes are 600 Oersted.
"1.4M" diskettes are about 750 Oersted.
It IS close (unlike 360K (300 Oersted) v 1.2M (600 Oersted)), and it
WILL work (unlike 360K v 1.2M), but it will NOT be as reliable as
using the correct diskette.
It's much more than that. Coating thickness (DS2D uses a thicker
coating than DSHD). Particle size (DSHD uses a smaller particle).
Loading (DS2D loads the binder more heavily).
If you've got one of each type, slide the shutter over and look at a
bright light through the cookie. Usually, you can see quite clearly
through DSHD media, but DS2D is almost always opaque.
Gotta be something to that...
I recall that some were even formatting DS2D media as DSED in the bad
old PS/2 days. Numerous claims of it working--but for only a short
time. DSED uses a barium ferrite formulation rather than an iron
oxide.
--Chuck
10:39 p.m.
On Monday (03/22/2010 at 05:54PM -0700), Fred Cisin wrote:
On 22/03/2010 19:18, Alex Taylor wrote:
So, does that mean that the 720K (600 Oersted) media requires a bigger
signal (ie, more write current) than the 750 Oersted 1.44M or the other
way around? It would seem that in one case you would be overdriving
the media and in the other case you might be underdriving it. Which way
is which?
Chris
--
Chris Elmquist
The idea was that reformatting a 1.44MB HD disk
in a DD drive will
leave traces of the original formatting behind (as they're always
preformatted for DOS/Windows), causing the unreliability. Using a bulk
eraser is meant to eliminate this problem, as it will turn them into
completely blank disks that can be formatted in a DD drive more
reliably.
In addition to all that, . . .
The coercivity (sorta like magnetic sensitivity) is WRONG.
"720K" diskettes are 600 Oersted.
"1.4M" diskettes are about 750 Oersted.
It IS close (unlike 360K (300 Oersted) v 1.2M (600 Oersted)), and it WILL
work (unlike 360K v 1.2M), but it will NOT be as reliable as using the
correct diskette. 
23 Mar
23 Mar
3:06 p.m.
In addition to all that, . . .
The coercivity (sorta like magnetic sensitivity) is WRONG.
"720K" diskettes are 600 Oersted.
"1.4M" diskettes are about 750 Oersted.
It IS close (unlike 360K (300 Oersted) v 1.2M (600 Oersted)), and it WILL
work (unlike 360K v 1.2M), but it will NOT be as reliable as using the
correct diskette.
Nowadays it is much easier to get HD disks than DD ones, which is a
problem users of old machines that never had an HD drive/controller. The
think I am thining of primarily are the HP 3.5" drives (both HPIB and
HPIL models), but of course there are many other machines.
I wonder if increasign the write current would help. It should only be a
matter of changing one resistor.
-tony
4:07 p.m.
On Tue, 23 Mar 2010, Tony Duell wrote:
Nowadays it is much easier to get HD disks than DD
ones, which is a
problem users of old machines that never had an HD drive/controller. The
think I am thining of primarily are the HP 3.5" drives (both HPIB and
HPIL models), but of course there are many other machines.
I wonder if increasign the write current would help. It should only be a
matter of changing one resistor.
Modifying the drive to use the other diskettes should work.
Would that be an increase or a decrease in the current?
But, you should keep a convenient way to switch back when using real DD
diskettes.
5241
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afra＠aurigae.demon.co.uk -
ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
chrise＠pobox.com -
cisin＠xenosoft.com -
pete＠dunnington.plus.com -
trixter＠oldskool.org