Very interesting.
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Floppy Drive - Wisdom needed.
- Thread starter smrieck511
- Start date
There is a significant difference between the density with HD and DD media.
From Herb's page (reminds me a lot of my writing: stuff tacked on top of stuff, repeated ad infinitum):
For the sake of argument let's throw in his Macintosh spec:
Looking at this wikipedia page, yeah I should have probably said bit density, not track density. It looks like the tracks are similar or identical in terms of angular length, but are packed denser.
Also check out this PDF by Teac. Have a look at page 11.
From Herb's page (reminds me a lot of my writing: stuff tacked on top of stuff, repeated ad infinitum):
Code:
3.5 inch drives, 720K (1MB) and 1.44M (2MB) and 2.88M (4MB)
(Earliest drives were Sony, single-sided. Most later drives were double sided.)
rotation speed: 300 RPM
track density 135 tpi;
80 tracks per side; IBM MS-DOS sectors per track 9, 18, 36 respectively
track 0 on outer circumference, track 79 innermost near hub.
head step angle 1.8 degrees
data frequency
250Kbps, MFM double density DD
500Kbps, MFM high density HD
1Mbps, ?MFM?? 2.88M extended density ED
innermost track bit density: 8717 bpi at 720K; 17,434 bpi at 1.44M; 34,848 at 2.88M
for MFM use; for FM use divide by 2
media: DD media is cobalt, 665 oersteds at 720K (1MB? unformatted); longitudinal recording;
HD media is 720 oersteds at 1.44M (2MB unformatted); longitudinal recording
ED is barium ferrite, [unconfirmed 1200 oersteds] at 2.88M (4MB unformatted), perpendicular recording
see Intel 82077SL (superdense floppy controller IC) for details.
single sided: r/w side is opposite label, "down" when drive mounted horizontally
track spacing: .0074 inches
drive track radius from center (inner to outer)
side 0 .9719 inches to 1.5551 inches
side 1 .9129 inches to 1.4961 inches
track width: .115 mm (.0045 inch) after "trim erase" on either side (not confirmed for 4MB format)
also see erase notes
orientation of index hole: none, inner diskette self-aligns with drive spindle
resistor terminator: resistor SIM, often soldered in,
note: 4MB standard created by Toshiba, endorsed by IBM. See AP-358, Intel reference below.For the sake of argument let's throw in his Macintosh spec:
Code:
3.5 inch drives Apple Macintosh, 400K, 800K (1MB) and 1.4M (2MB)
note: 20-pin controller interface versus 34-pin
rotation speed: under software control, 394-590 RPM, see below
track density: probably same as other 3.5" floppy drives
80 tracks per side; only 400K drive is single-sided
track 0 on outer circumference, track 79 innermost near hub.
head step angle: unknown
data frequency: see below, otherwise for MS-DOS same as MFM 720K/1.44M standards
media: same as 3.5" double-density 360K, and 3.5" High-density 1.44M
single sided: r/w side is opposite label, "down" when drive mounted horizontally
orientation of index hole: none, disk media self-aligns with drive spindle
resistor terminator: unknown
source for information: various documents referenced in http://68kmla.org/forums/
look for discussions of "Macintosh floppy drive rotation speed"
Apple document "Double-Density versus High-Density Disks"
describes 400K and 800K as GCR encoded, and 720K and 1.44MB MS-DOS as MFM.
Apple GCR encodes four data bits into five recorded bits at higher density.
For uniform GCR data density per inch, track speed varies as follows.
800K tracks 0-15 at 394 RPM and 12 sectors per track (innermost)
16-31 429 11
32-47 472 10
48-63 525 9
800K tracks 64-79 at 590 RPM for 8 sectors per track
(simple math says 800 sectors X 2 sides for 800K => 512 bytes/sector)
1.44MB MFM is 300 RPM for 18 sectors/track all 80 tracksLooking at this wikipedia page, yeah I should have probably said bit density, not track density. It looks like the tracks are similar or identical in terms of angular length, but are packed denser.
Also check out this PDF by Teac. Have a look at page 11.
Thanks for that research. If the media is different, does this necessarily mean the heads are different?
My next step will be to replace the head assembly (temporarily) with one from a known working superdrive and see if things change.
My next step will be to replace the head assembly (temporarily) with one from a known working superdrive and see if things change.
I suspect they're compatible. Just that the disks are different.
"A recap/update:
It now successfully formats, verifies and mounts 800k disks (two-sided) in one shot (without having to format one side first).
It appears to format 1.44mb disks but immediately fails/ejects on verification with every disk I've tried (about a dozen) that work fine in other drives."
I think you are still a slight bit out with the alignment, the fact that it works now with 800k disks suggests that it can be fixed
It now successfully formats, verifies and mounts 800k disks (two-sided) in one shot (without having to format one side first).
It appears to format 1.44mb disks but immediately fails/ejects on verification with every disk I've tried (about a dozen) that work fine in other drives."
I think you are still a slight bit out with the alignment, the fact that it works now with 800k disks suggests that it can be fixed
It seems to be able to format, verify and mount 800k disks no matter where I put the ZTS.
Still fails at verification for all 1.44mb disks.
Still fails at verification for all 1.44mb disks.
Well, I replaced the head assembly on the drive in question with a head assembly from another known working HD Drive.
Drumroll................
It formats, verifies and mounts 1.44mb HD disks now.
So the problem in this case, was not the ZTS but apparently the heads themselves or maybe the ribbon cables. Still curious why the damaged heads work fine with 800k disks though.
Drumroll................
It formats, verifies and mounts 1.44mb HD disks now.
So the problem in this case, was not the ZTS but apparently the heads themselves or maybe the ribbon cables. Still curious why the damaged heads work fine with 800k disks though.
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Yeah I've learned alot about these in the past few days. What crazy cool contraptions! Thanks all.
Probably the magnets are accurate enough for 800k bands, but not for HD bands. I remember having this issue crop up eventually with read/write heads for audiocassette players, where you'd start to get some crosstalk between the stereo bands.
Do they look different? Not in my opinion at a glance. Wonder what he's referring to?
Not to throw another wrench into things, but I've successfully swapped 800K heads into HD drives on numerous occasions to fix troublesome HD drives. They appear to work fine. Perhaps the heads are different, but are engineered with tolerances that make them compatible. Happy accident if that's the case.
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