Subject: Re: Putting tapes in varblock mode
To: Objects In Mirror Are Closer Than They Appear <firstname.lastname@example.org>
From: John F. Woods <jfw@FunHouse.com>
Date: 04/01/1996 21:45:36
> > QIC does tend to have better movement support than 8mm...
> I think you have this backwards. I have yet to encounter a QIC which
> will support BSR/BSF, while I have yet to encounter an 8mm which won't.
Archive VIPER QIC-150 does at least BSR and I think BSF. The backspace
command is about 1% the speed of a forward read, however (it has to read
the block backwards, BIT REVERSE IT, then check to see if the checksum is
OK and what the current block number is -- bleah!).
I went to a great deal of effort in an old tape driver to figure out whether
a given seek was faster with backspace commands or rewind and forward space...
(Though I think the code was a little off, since the time to rewind is not
linearly proportional to block number.) I know the QIC drives I used before
that didn't have backspace, though, and I haven't studied any QIC drives