11 Jun
2004
11 Jun
'04
8:34 a.m.
On Jun 11, 14:44, Jules Richardson wrote:
The information I have gives the makeup of each of the gap types in
terms of bit patterns, counts, what clock transitions are missing for
MFM formats etc.
Question is, is this a standard? I mean, for any disk using MFM or FM
recording are these bit patterns going to be the same? Or is it
dependant on the controller chip being used?
So long as it's FM/MFM it's pretty much the same for any controller --
otherwise disks wouldn't be so interchangable :-)
If you want an external floppy, why go to a lot of effort when all you
need is one of the old cards that had an external connector? It's
normally a 37-pin D-connector, with a few pins used to supply the
power. Of course they're ISA cards, so you'd need a machine with ISA
slots, but your reference to "ISA bus hang-ups" implies you have that.
You also need to be able to set the card to be the second floppy
controller (but most of the ones with external connectors have that
capability) or disable the on-board floppy controller (if there is one
-- but most older boards can do that too).
--
Pete Peter Turnbull
Network Manager
University of York
11 Jun
11 Jun
8:50 a.m.
>>>> "Pete" == Pete Turnbull
<pete(a)dunnington.u-net.com> writes:
Pete> On Jun 11, 14:44, Jules Richardson wrote:
> The information I have gives the makeup of each of
the gap types
> in terms of bit patterns, counts, what clock transitions are
> missing for MFM formats etc.
>
> Question is, is this a standard? I mean, for any disk using MFM or
> FM recording are these bit patterns going to be the same? Or is it
> dependant on the controller chip being used?
Pete> So long as it's FM/MFM it's pretty much the same for any
Pete> controller -- otherwise disks wouldn't be so interchangable :-)
I'm not sure about all the context of this question anymore, but...
The number of tracks may be fixed; the number and size of sectors is
not. Standard PC floppies have 9 sectors per track, but RX50 floppies
have 10. You can read and write RX50s on a PC, but it's not a simple
matter. (I found out, long ago, when I wrote a RSTS file interchange
program for Linux and DOS.)
paul
10:52 a.m.
On Fri, 11 Jun 2004, Pete Turnbull wrote:
So long as it's FM/MFM it's pretty much the
same for any controller --
otherwise disks wouldn't be so interchangable :-)
With a few quirks and a few exceptions, such as Amiga, which is MFM, but
is NOT an "IBM 3740"/"WD" style sector.
If you want an external floppy, why go to a lot of
effort when all you
need is one of the old cards that had an external connector? It's
normally a 37-pin D-connector, with a few pins used to supply the
power. Of course they're ISA cards, so you'd need a machine with ISA
slots, but your reference to "ISA bus hang-ups" implies you have that.
Some have power on the DC37, some don't.
The IBM 5150 FDC did NOT supply power on the external
floppy connector. When IBM sold an external 3.5" 720K
drive for it, there was a second cable to go through a
hole in the back and connect to the power supply
You also need to be able to set the card to be the
second floppy
controller (but most of the ones with external connectors have that
capability) or disable the on-board floppy controller (if there is one
-- but most older boards can do that too).
or just cable the existing controller to an external connector.
IBM had an adapter for AT's and one for PS/2's for that.
There was once a serial external "PC 5.25 drive" for Macintosh!
It was actually a floppy drive and an AMPRO littleboard
in a case with serial port connection. When coupled to
a Mac, and running its software, it could read PC and
some CP/M diskettes. Just like any other computer connected
to the serial port. But Mac users would NOT buy a PC
compatible computer for doing their file transfers, so
it was sold as being a "smart disk drive"
--
Grumpy Ol' Fred cisin(a)xenosoft.com
14 Jun
14 Jun
6:40 a.m.
> Question is, is this a standard? I mean, for any disk using MFM or FM
> recording are these bit patterns going to be the same?
Standards schmandards, we have lots of standards!
If you want to read any possible floppy format, then the only thing you
can rely on is transitions to/from 0/1, and the DSP approach is about
right.
As others point out, the WD chips are the sloppiest in terms of what
their state machines insist on the NEC 765 is a pain.
PS: The old Micromation floppy controller (CP/M 1.4 days) used NEITHER
chip family, did their own formatin LS TTL, and practically no one can
read them.
You can probably do all this in a PC sound card these days!
6:57 a.m.
On Mon, 2004-06-14 at 18:40, Tom Jennings wrote:
That does seem to be the case from what others have said so far.
I should have actually made myself a bit clearer - in that I'm only
interested in backing up floppies and being able to restore them later.
I don't need to actually understand the contents on the machine which is
performing the backup.
Having said that, I'd rather not have each floppy take up several
megabytes due to overampling of the data stream - so I do still need to
make sense of bit transitions and record those.
"being able to restore them later" is perhaps a seperate project - I'd
be almost content just knowing that I had a copy of the raw data from a
floppy in the event of failure, even if currently I had no way of
restoring it.
Being able to do this from one platform, at least for any FM/MFM encoded
soft-sectored floppy (which for me is what 99% of my collection uses) is
pretty desirable. If I had room I'd have all my machines set up and laid
out - but as it stands nearly everything has to reside stored away,
which means it's a pain to do anything as soon as some new software
lands on the doorstep.
cheers
Jules
> Question is, is this a standard? I mean, for any disk using MFM or FM
> recording are these bit patterns going to be the same?
Standards schmandards, we have lots of standards!
If you want to read any possible floppy format, then the only thing you
can rely on is transitions to/from 0/1, and the DSP approach is about
right. 
12:10 p.m.
PS: The old Micromation floppy controller (CP/M 1.4
days) used NEITHER
chip family, did their own formatin LS TTL, and practically no one can
read them.
I have a Micromation Doubler in my CASU Super C (S100 bus CP/M machine).
From what I rmemeber the single-density (FM) format is
standard, and can
read/write IBM3740 disks. The double density format, though, is
probably
unique to this card.
You can probably do all this in a PC sound card these
days!
Not many sound cards will handle 500kHz signals, surely?
-tony
15 Jun
15 Jun
8:10 a.m.
On Mon, 2004-06-14 at 17:10, Tony Duell wrote:
Who knows! What was once impossible is now routine, or worse, obsolete
:-)
I have a Micromation Doubler in my CASU Super C (S100
bus CP/M machine).
The Doubler! I forgot about that!! You're right of course, the DD format
for the DOubler was it's downfall, it was built for 128 byte sectors,
period, and being all-hardware wasn't programmable. WD chips killed it I
guess.
From what I rmemeber the single-density (FM)
format is standard, and can
read/write IBM3740 disks. The double density format,
though, is probably
unique to this card. You can
probably do all this in a PC sound card these days!
Not many sound cards will handle 500kHz signals, surely?
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participants (6)
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ard＠p850ug1.demon.co.uk -
cisin＠xenosoft.com -
julesrichardsonuk＠yahoo.co.uk -
pete＠dunnington.u-net.com -
pkoning＠equallogic.com -
tomj＠wps.com