On Mon, Oct 28, 2024 at 7:22 PM Fred Cisin via cctalk
<[email protected]> 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
