15 Dec
2005
15 Dec
'05
6:18 p.m.
Subject: RE: Early 3.5" Floppy Drives
From: "Chuck Guzis" <cclist at sydex.com>
Date: Thu, 15 Dec 2005 09:32:54 -0800
To: cctalk at classiccmp.org
On 12/15/2005 at 7:42 AM Allison wrote:
;) your assumption is double density. 8" SSSD is not that fast.
I never said formats were the same or even dive interface only that
the data rates fly.
765A write clock rate by drive and density, bit rate is clock/2.
Size density format writeclock
-----------------------------------
8" DD MFM 1000khz
8" SD FM 500khz (8"SSSD 241k CP/M standard)
5.25 DD MFM 500khz (40track is 360k, 80track 720k)
5.25 SD FM 250khz
3.5" HD MFM 1000khz (1.44mb) (looks like 8" different CHS)
3.5" DD MFM 500khz (720k) (same rate as 5.25 DD and 8" SD)
3.5" ?? FM 250khz (not used obsolete)
None of this has anything to do with rotation rate of the media.
Actual data storage capability is format dependent.
One example that was known the to CP/M world was 5.25" 80track (FD55F)
two sided at either 720k or ~780k I was sometimes called QD as it
was really the same as the 360k but twice the tracks (48 tpi vs 96).
So happens that the 3.5" drive can be plugged in and used exactly
as if it were a FD55F for the same 720k as I do it all the time
Any PC controller that can do 720k 3.5"
format can do
8" as it's the same data rate. it's not what chips was
used it's how it was used.
Whoa. Sorry, I couldn't let this one go by unanswered.
8" drives use a 500K data clock rate, not 250K like the DS2D 720K 3.5". A
controller that supports 1.44M DSHD 3.5" should do just fine on 8". While
there were early 8" drives that used a lower clock rate, they were pretty
much gone by the time of the dawn of the PC. FM support with a modern
controller is a somewhat different kettle of fish. The nearest AT medium
to the 8" drive would be the 5.25" high-density diskette, which also spins
at the same rate--360 RPM. from a CP/M system to DOS and the CPM80 side has a
utility that
read/writes DOS FAT files. I'd have used 1.44 but the WD1770
literally
cannot run at the required rate (not rated to either!).
I'll let you all in on a dirty trick. The 765(A) outputs a signal on
pin26 called FM, that is used to select data rates /2 ALWAYS. If you lift
the pin the data rates for FM mode are now twice as fast and suitable
for many other uses like 8" media. For the integrated flavors of 765
the same effect can be had by twiddling bits in the drive control register.
If all else fails, you can double the the 8 or 16 mhz clock source
used to 16/32 as needed. I have taked the 9.6mhz out and used higher
on one board 16mhz so that switching to AT 5.25HD got me 8"DD instead
without futzing with drivespeed (rotation rate) that means nothing to
most 3.5, 5.25 (including FD55GFR with the jumper pulled) and 8" drive.
That was the beauty of the NEC APC line--from 8"
right down to 3.5", the
data format didn't vary one iota. The NEC 9801 floppies still record 1.3MB
on a 3.5" drive spinning at 360 RPM.
But the PC-XT 8" drive controllers were a special beast, honest.
Not really. I can take the stock IBM XT long board and with one change
make it do DSDD 8" (other than cable adaptor). Common parts cost 'bout
$1, acutally cheaper now than 20 years ago then it would have been 1.89.
Replace the 8mhz clock source with 16mhz.
Thats how it's done.
Allison
15 Dec
15 Dec
6:40 p.m.
Rumor has it that Allison may have mentioned these words:
[snippety]
Size density format writeclock
-----------------------------------
8" DD MFM 1000khz
8" SD FM 500khz (8"SSSD 241k CP/M standard)
5.25 DD MFM 500khz (40track is 360k, 80track 720k)
5.25 SD FM 250khz
3.5" HD MFM 1000khz (1.44mb) (looks like 8" different CHS)
3.5" DD MFM 500khz (720k) (same rate as 5.25 DD and 8" SD)
3.5" ?? FM 250khz (not used obsolete)
3.5" FM was used for microcomputers - the Tandy Portable Disk Drive (OEMmed
by Brother, IIRC) was 40 tracks, 2SPT FM w/100K storage. Serial port
driven, and worked with the Tandy Model 100/102/200 laptops. In my Service
manual for the critter, it did mention the density, but I don't have that
handy. DD disks worked just fine on it (read: data life at least into the
10 year range), but HD didn't work so well, IIRC.
The TPDD2 was also FM, but used an 80 track drive (set into 2 banks for
compatibility with the TPDD1) for 200K storage.
Laterz,
Roger "Merch" Merchberger
--
Roger "Merch" Merchberger -- SysAdmin, Iceberg Computers
_??_ zmerch at 30below.com
(?||?) If at first you don't succeed, nuclear warhead
_)(_ disarmament should *not* be your first career choice.
7:30 p.m.
On 12/15/2005 at 1:18 PM Allison wrote:
;) your assumption is double density. 8" SSSD is
not that fast.
I never said formats were the same or even dive interface only that
the data rates fly.
Nope. I'm just going by the 765 data sheet:
"Pin 19 - CLK - Single-phase 8 MHz (or 4 MHz for mini-floppies) squarewave
clock"
IOW, if you supported 3.5 DD (or SD) floppies, you weren't going to be
able to do an A1 8" floppy without changing the clock.
Same thing obtains for the WD 179x - "Pin 24 - CLOCK - This input requires
a free-running 50% duty cycle square wave clock for internal timing
reference. 2 MHz +/- 1% for 8" drives, 1 MHz +/- 1% for mini-floppies."
The 279x has a clock divider that's programmed by pin 17 (5/8).
Look at the grandaddy of the 8" XT drive controllers, the CompatiCard I.
It uses port 7F2H to change the 765 clock from 4 to 8 MHz for 8" support.
MFM/FM doesn't enter into the equation--that's programmed into the read and
write commands and the data separator.
But an old XT-era 720K 3.5"/5.25" controller couldn't do this
clock-switching trick unless it could also support 1.2/1.44 media.
Cheers,
Chuck
765A write clock rate by drive and density, bit rate is clock/2.
Size density format writeclock
-----------------------------------
8" DD MFM 1000khz
8" SD FM 500khz (8"SSSD 241k CP/M standard)
5.25 DD MFM 500khz (40track is 360k, 80track 720k)
5.25 SD FM 250khz
3.5" HD MFM 1000khz (1.44mb) (looks like 8" different CHS)
3.5" DD MFM 500khz (720k) (same rate as 5.25 DD and 8" SD)
3.5" ?? FM 250khz (not used obsolete)
None of this has anything to do with rotation rate of the media.
Actual data storage capability is format dependent.
One example that was known the to CP/M world was 5.25" 80track (FD55F)
two sided at either 720k or ~780k I was sometimes called QD as it
was really the same as the 360k but twice the tracks (48 tpi vs 96).
So happens that the 3.5" drive can be plugged in and used exactly
as if it were a FD55F for the same 720k as I do it all the time
from a CP/M system to DOS and the CPM80 side has a utility that
read/writes DOS FAT files. I'd have used 1.44 but the WD1770 literally
cannot run at the required rate (not rated to either!).
I'll let you all in on a dirty trick. The 765(A) outputs a signal on
pin26 called FM, that is used to select data rates /2 ALWAYS. If you lift
the pin the data rates for FM mode are now twice as fast and suitable
for many other uses like 8" media. For the integrated flavors of 765
the same effect can be had by twiddling bits in the drive control
register.
If all else fails, you can double the the 8 or 16 mhz
clock source
used to 16/32 as needed. I have taked the 9.6mhz out and used higher
on one board 16mhz so that switching to AT 5.25HD got me 8"DD instead
without futzing with drivespeed (rotation rate) that means nothing to
most 3.5, 5.25 (including FD55GFR with the jumper pulled) and 8" drive.
That was the beauty of the NEC APC line--from
8" right down to 3.5", the
data format didn't vary one iota. The NEC 9801 floppies still record
1.3MB
on a 3.5" drive spinning at 360 RPM.
But the PC-XT 8" drive controllers were a special beast, honest.
Not really. I can take the stock IBM XT long board and with one change
make it do DSDD 8" (other than cable adaptor). Common parts cost 'bout
$1, acutally cheaper now than 20 years ago then it would have been 1.89.
Replace the 8mhz clock source with 16mhz.
Thats how it's done.
Allison 
11:19 p.m.
On Thu, 15 Dec 2005, Allison wrote:
765A write clock rate by drive and density, bit rate
is clock/2.
Size density format writeclock
-----------------------------------
8" DD MFM 1000khz
8" SD FM 500khz (8"SSSD 241k CP/M standard)
5.25 DD MFM 500khz (40track is 360k, 80track 720k)
5.25 SD FM 250khz
3.5" HD MFM 1000khz (1.44mb) (looks like 8" different CHS)
3.5" DD MFM 500khz (720k) (same rate as 5.25 DD and 8" SD)
3.5" ?? FM 250khz (not used obsolete)
one more entry to add to that table:
5.25 "HD" MFM 1000KHz (1.2M) (looks like 8", could be SAME
CHS)
None of this has anything to do with rotation rate of
the media.
Very true. 8" and "1.2M" is 360RPM, all others are 300
RPM,
with a few exceptions (early Sony 3.5 at 600 RPM, NEC, Weltec, etc.)
Actual data storage capability is format dependent.
and the format choices open an even bigger can of worms
One example that was known the to CP/M world was
5.25" 80track (FD55F)
two sided at either 720k or ~780k I was sometimes called QD as it
was really the same as the 360k but twice the tracks (48 tpi vs 96).
So happens that the 3.5" drive can be plugged in and used exactly
as if it were a FD55F for the same 720k as I do it all the time
from a CP/M system to DOS and the CPM80 side has a utility that
read/writes DOS FAT files. I'd have used 1.44 but the WD1770 literally
cannot run at the required rate (not rated to either!).
I'll let you all in on a dirty trick. The 765(A) outputs a signal on
pin26 called FM, that is used to select data rates /2 ALWAYS. If you lift
the pin the data rates for FM mode are now twice as fast and suitable
for many other uses like 8" media. For the integrated flavors of 765
the same effect can be had by twiddling bits in the drive control register.
If all else fails, you can double the the 8 or 16 mhz clock source
used to 16/32 as needed. I have taked the 9.6mhz out and used higher
on one board 16mhz so that switching to AT 5.25HD got me 8"DD instead
without futzing with drivespeed (rotation rate) that means nothing to
most 3.5, 5.25 (including FD55GFR with the jumper pulled) and 8" drive.
--
Fred Cisin cisin at xenosoft.com
XenoSoft http://www.xenosoft.com
PO Box 1236 (510) 558-9366
Berkeley, CA 94701-1236
That was the beauty of the NEC APC line--from
8" right down to 3.5", the
data format didn't vary one iota. The NEC 9801 floppies still record 1.3MB
on a 3.5" drive spinning at 360 RPM.
But the PC-XT 8" drive controllers were a special beast, honest.
Not really. I can take the stock IBM XT long board and with one change
make it do DSDD 8" (other than cable adaptor). Common parts cost 'bout
$1, acutally cheaper now than 20 years ago then it would have been 1.89.
Replace the 8mhz clock source with 16mhz.
Thats how it's done.
Allison
11:55 p.m.
Fred Cisin wrote:
It sounds upside down to me. The 300rpm 1.2mb gets you a standard data rate
500kbS(1mhz clock) and the 360 gets you the 600kbS rate (1.2mhz clock).
I really try to shun that pile from my mind.
the general game with spindle speed was one of to cases, lower latency
(spin faster) or play games with data rate without altering the controller
logic. Maybe even both. No question a 600rpm spindle would get your data
around sooner.
Allison
On Thu, 15 Dec 2005, Allison wrote:
I wanted to leave that sick puppy out of it (along with 2.88mb).
The CHS could be the same, save for 8" DD was often different.
765A write clock rate by drive and density, bit
rate is clock/2.
Size density format writeclock
-----------------------------------
8" DD MFM 1000khz
8" SD FM 500khz (8"SSSD 241k CP/M standard)
5.25 DD MFM 500khz (40track is 360k, 80track 720k)
5.25 SD FM 250khz
3.5" HD MFM 1000khz (1.44mb) (looks like 8" different CHS)
3.5" DD MFM 500khz (720k) (same rate as 5.25 DD and 8" SD)
3.5" ?? FM 250khz (not used obsolete)
one more entry to add to that table:
5.25 "HD" MFM 1000KHz (1.2M) (looks like 8", could be SAME
CHS) None of this
has anything to do with rotation rate of the media.
Very true. 8" and "1.2M" is 360RPM, all others are 300 RPM,
with a few exceptions (early Sony 3.5 at 600 RPM, NEC, Weltec, etc.)
6964
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4 comments
4 participants
participants (4)
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ajp166＠bellatlantic.net -
cclist＠sydex.com -
cisin＠xenosoft.com -
zmerch＠30below.com