Disk TPI's

From: Brett <danjo_at_xnet.com>
Date: Mon Sep 1 14:53:58 1997

On Mon, 1 Sep 1997, Tim Shoppa wrote:
> > out there? Anyone know of any online resources for this info? I checked
> > the Accurite home page and they only mention (at least as far as I could
> > find) 48, 96, and 135 TPI for the 3 1/2" and 5 1/4" drives. What about the
> > 8" drives
>
> All the 8" drives I ever met were 77-track devices, at (I believe)
> 48 TPI. Depending on the recording density, you could get anywhere
> between:

Yup 48 TPI was about it.

> FM, 128 bytes/sec: 26 sectors * 77 tracks * 128 byte/sec = 256256 bytes.
>
> and
>
> MFM,1024 byte/sec: 8 sec * 77 tracks * 1024 byte/sec * 2 sides = 1261568 bytes
>
> for soft-sectored drives.

On my CP/M system I put 1.6Mb on 8" floppies - let me see now - I think
it was 512 byte sector * 21 sectors * 77 tracks * 2 sides. This was
achieved by changing the intersector gap and making it REALLY tight on
end of track to Index spae as well 8-) But it was neat to have 6.5Mb of
floopy storage!

> Some early histories of the floppy disk report an IBM 8" format that
> only had about 100Kbytes on it. I have no idea if this used the
> same 77-track spacing with a different sectoring, or what. This format
> certainly wasn't in wide use by 1974; all my floppies from 1974
> are in the standard IBM 3740 26*77*128 format.

I think this was before they *invented* the trim erase on the head. It
made them use somethng like double the track spacing.

BC
Received on Mon Sep 01 1997 - 14:53:58 BST