29 Oct
2024
29 Oct
'24
12:25 p.m.
On Mon, Oct 28, 2024 at 7:22 PM Fred Cisin via cctalk
<cctalk(a)classiccmp.org> wrote:
Track width
360K drives (40 track) have tracks 48 tpi. (Early on, Shugart SA400, and
For the pedants, the IBM 360K format is 80 track. 40 cylinders, each
of 2 tracks, one on each side of the disk.
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.
There were a few 100tpi 5.25" drives. Annoying because they couldn't
read 40 cylinder disks even if you double-stepped them. Didn't
Commodore use them in the 8050?
3.5" drives tend to be 80 cylinder, 135 tpi. There were a few 40
cylinder 67.5 tpi drives with, I assume, a wider head. I've never seen
one in a PC though.
The spec I can find for the 40 cylinder 3" drive says it's 100tpi. So
I assume the 80 cylinder one (often used as a second drive on Amstad
PCW's) would be 200tpi.
(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.
I've done this many times, mostly to write 40 cylinder CP/M disks on
80 cylinder drives. I use a bulk-erased disk, format and write on the
80 cylinder drive then copy it to a fresh 40 cylinder disk on the
target machine. Never had any problems doing that.
-tony