27 Feb
2023
27 Feb
'23
3:50 p.m.
> Then, I made the students describe how to make a
48tpi disk with a 96tpi
> drive.
Whether to count their answers as acceptable or not was mostly just the
understanding of need for "bulk erase"/"virgin disk"
On Mon, 27 Feb 2023, Chuck Guzis via cctalk wrote:
One thing that folks need to bear in mind is that
it's the change of
direction of magnetization that induces a signal in a drive head. So a
DC or AC erase on the "straddling" portions of a track will work equally
as well.
There is some erasing done by the heads to clear some of the area around
the track. BUT, that erase of a 96tpi head is not wide enough to remove
all traces of a previous 48tpi recording.
I wondered why they didn't incorporate TWO sets of erase heads in 1.2M
drives, so that it could "clear the margins" enough for 96tpi OR 48tpi
re-writing.
Could you explain [in dumbed down form], the differences between "tunnel
erase" and "straddle erase"? Is it solely that the erase head(s) are
behind, VS alongside the R/W head?
I looked at
http://www.bitsavers.org/pdf/cdc/discs/floppy/75897469_5inchFDD_Fmt_Jan80.p…
but I don't understand all of it.
--
Grumpy Ol' Fred cisin(a)xenosoft.com