Random Access Tape 2459

Peter Flbutt

Not to my knowledge. Yes, Multics standard tape format had a block number in each block, and the tape DIM noticed an error if the number was not monotone increasing. It did not provide this block number to its caller, and the hierarchy backup software did not record the block number in the dump map, and the retriever-reloader software did not try fancy positioning tricks to find a particular file.

The tape format described in had some cool attributes though. If an error occurred when writing a tape block, the tape DIM just wrote the block again, with the same block number. To read a block, it read until past the desired block. This meant that while a tape was reading, an operator could put the drive in standby, dismount the tape, mount it on another drive, switch unit numbers, and ready the new drive: and the tape DIM would notice the block number mismatch, resynch, and

Multics tape format was also specified to have a single tape mark every 128 blocks, so that spacing forward to a given record number would be fast. We never used this feature and I think after a while eliminated it: it just made it difficult to copy a Multics tape on a 360.