28 Oct
2024
28 Oct
'24
7:22 p.m.
Track width
360K drives (40 track) have tracks 48 tpi. (Early on, Shugart SA400, and
Apple SA390, only used 35 of those tracks) That's about 1/2 mm from
center of one track to center of the next. The track itself is about
1/3 mm wide, leaving a little blank space between tracks.
80 track (both 1.2M, and 5/25" 720K/800K) have tracks 96 tpi. that's about
1/4 mm from center of one track to center of the next. The track width is
about 1/6 mm.
(BTW, 8" disks are 48tpi)
It is possible to use a 1.2M drive to make a usable 360K disk,
Use the right ("360K"/300 Oersted) diskette. DO NOT USE A 1.2M DISKETTE!
Start with a thoroughly bulk eraased or virgin disk that is NOT "preformatted"
The 1.2M drive will have to "double step" to get 40 tracks at 48tpi
The drive must not be using the HD write current (I've no idea of amperage)
The drive must switch to 300 RPM at 250K bps, or switch to 300 bps at 360 RPM
The resulting diskette will have narrower tracks than normal, which is
usually not a problem, but the tracks will be at the right spacing.
DO NOT "RE-WRITE", nor "RE-FORMAT" a 360K diskette in a 1.2M drive
unless
you throughly bulk erase it.
When you RE-WRITE a 360K diskette in a 1.2M drive, it already has wide
tracks, and the 1.2M drive will write a narrow track down the middle of
each. It will still be quite readable with the 1.2M drive.
BUT, a 360K drive, instead of finding a wide track, finds a wide track
with a narrow track down the middle of it! (and tiny gaps alongside the
narrow track) It can't read that.
By analogy, a bike caan ride down the middle of a car tire track rut, and
two bikes can go side by side in the two ruts.
But, if you try to analyze the tread pattern, it's different in the
middle than away from the middle, and won't match anything.
On fresh mud, two bikes at the right distance apart can make a pair of
rute that looks like a car with narrow wheels.
(a 5.25" "720K/800K/"quad density" drive has the same problem)
(BTW, "quad density" is a marketing obfuscation. It is still double
density, but with more tracks, conflating disk total capacity with linear
density. It is not a change in the linear density.)
(BTW, Superbrain (intertec?) when the changed from SSDD to DSDD called the
two sided same density, "QUAD DENSITY"! But, then later when they went to
80 track DSDD, which many companies called "Quad density", they couldn't
call it that, because they had alread used that term. So, they called it
"SUPER DENSTY"! and abbreviated that SD (which means FM/single-density to
everybody else))
If you do tackle the Herculean task of converting a 1.2M drive into a 360K
drive, be aware that that will have abnormally narrower heads!
--
Grumpy Ol' Fred cisin(a)xenosoft.com