13 Dec
2014
13 Dec
'14
11:02 a.m.
On 12/13/2014 01:36 AM, John Wilson wrote:
On Fri, Dec 12, 2014 at 11:04:20PM -0600, Jon Elson
wrote:
No, you
could commence writing after any existing record,
and the drive would take
care of the mess that was similar to a punch-in edit on
videotape, if you remember
what that looked like on the early VCR's. It would just
overwrite the following data
for about 2-3 seconds with full-width erase, and then pick
up writing in cleanly-erased
tape. I think some of the later drives might have been able
to do better with flying
erase heads. But, we generally never did fancy stuff with
them, just write a whole
tape at a time. Anyway, we never added records to an
existing file, but did often
add new files after the double file mark.
Jon
I worked with some Exabyte
drives and others that had a lot of constraints on what you could do,
and you could do some interesting things.
My recollection with the Exabyte 8mm
drives was that they would let you
write new data after the last thing written, but you couldn't backspace and
write over existing data, unless you were rewinding all the way to BOT. So
they were lousy at emulating 9-tracks (but some controllers fixed that by
wrapping everything in headers and writing their own suffix records that
said when to disregard the last N blocks, and they'd read ahead by some
known amount looking for that, to at least handle the common case of going
to LEOT, backspacing between the two tape marks, and writing a new file).