Letters to the Editor
HS-1N Micro Cassette
Adrian Perkins writes in the
March-April 1984 issue of 80-BUS News
defection from HS-1N to disk,
and mentions a problem with ageing drives.
As co-designer of the project, I have been using the same two drives regularly
since 1980, and have found them remarkably reliable – hence I have not yet
succumbed to the pressure to move to disks. They do, however, tend to drift
away from the specified speed with age, and difficulties may arise when an old
tape is edited.
HS-1N tapes are initialised by writing a blank catalog at the beginning
of the tape; apart from this the tapes are not formatted in any way. At this
stage all 28 remaining 2k blocks are available, and when a file is saved the
blocks at the beginning of the tape are filled first, always back-spacing one
block and running forwards before writing the next block (to allow for a
check-read and to get the tape running up to a consistent speed).
If large files are used (say 20k source files, occupying 10 HS-1N blocks
on tape) then it may be possible to fit only two on one side of a tape. When
the first file is deleted, blocks 1 to 10 on the tape are released for re-use,
and if the drive is running at a different speed corruption may take place.
The most likely problem to arise involves a slowing of the drive. In this
case, when ten new blocks are saved there may be a residue of the original
tenth block which is not overwritten by the new tenth block. Attempts to read
the eleventh block (the first block of the original second file) may fail
because of this, but you may be able to recover by advancing the tape over the
Read the new file in the normal way (tape stops after block 10), using
Return control to NAS-SYS.
Run the tape forward a fraction by entering O 78 1 and O 78 0 one after
the other (previously set up on the screen using the cursor keys). Use O
F8 1 and O F8 0 if yours is one of the earliest HS-1Ns.
Warm start HS-1N (E D003).
Try to load the “lost file” in the normal way.
If the drives are running faster than before, the tenth block of the new
file may overwrite the first block of the previous one, and this block is
therefore lost for ever. By using the above technique, and editing the HS-1N
catalogue workspace, you may be able to recover the later blocks. Data loss
from fast drives is less likely than difficulties with slow drives, as the new
file must extend across the entire inter-block gap on the tape, before it can
corrupt the next block.
I should stress that there is no need to worry about reading tapes from a
slow drive on a fast one, or vice-versa, only about editing tapes on a drive
with a different speed. It is best to use a blank (either new or deleted) tape
when saving edited versions of old files.
Yours sincerely, Dr M.D. Hendry, Cupar, Fife.
Lucas, NasDos, and Colour
Perhaps the following news/viewpoints would be of interest:–
a) There have been several recent letters suggesting that Lucas are not very
helpful on some occasions. I can only say that over the last 6 months or so,
I have written to them 3 times asking for help or information on various
topics, and on each occasion I have received a courteous and helpful response.