21 May
2001
21 May
'01
2:21 p.m.
Tony Duell wrote:
The commodore
tape drive system apparently put a header at the start of each
file. You could fast forward through the tape manually until you got to about
Yes, most systems did that. The home computers using normal audio tapes
(that you had to position manually) generally had a header per file. The But if you don't have automatic fast forward (and
some way to judge the
approximate postiion of the tape automatically), then finding a
particular file is consists of rewinding the tape to the start and then
reading the tape (at normal speed) until you find the file you want.
Which, using one side of a C90 cassette, could take 45 minutes. This is
going to get boring fast.
Oops, interesting conversation you have here. I used C90 cassettes or
whatever in my datasette and I could position the thing quite
easily using the mechanic position counter. Didn't you have that
on your device? May be the PET 2001 didn't have a counter, but the
datasette I got with my C=64 did have that counter. The counter
wouldn't work accross two different devices, the one in school
counted at different speed than the one I had at home ... but I
suppose I could have found a conversion factor if need had been.
Now, for the more modern times, a 2GB DAT tape doesn't have a counter
and doesn't have a directory. But it has a start-of-file marker
that you can fast forward to (at amazing speeds!). You can do the
same backwards and on a per-block basis. On UNIX with "mt fsf $n"
you can forward by $n number of files. I found it impossible to
update a directory at the start of the tape, since each write would
leave an end-of-tape-mark at the end so that the rest of the tape
was lost. So, again I use the simple manually kept directory with
a pencil and the tape cover/label.
-Gunther
--
Gunther Schadow, M.D., Ph.D. gschadow(a)regenstrief.org
Medical Information Scientist Regenstrief Institute for Health Care
Adjunct Assistent Professor Indiana University School of Medicine
tel:1(317)630-7960 http://aurora.regenstrief.org