[cctalk] Re: Age of Tape Formats?

Speaking of compatibility, we had a 360/50 many ages ago, and it was "permitted" to put the tape controller on the multiplexer channel.  This prevented long tape operations from locking up the disk controller on the selector channel.  The model /50 only had one selector.  But, if there was too much traffic on the multiplexer, it could cause data late issues.  We tried to read some of those tapes on our PDP-11, and the controller couldn't do it.  I got some Magna-See, and found that there were little gaps in the data records. These were quite obvious visually, so at least several character spaces.  Apparently, IBM's tape controller had a 2-character FIFO and would only start processing the end of record after a LONG gap of at least 5-10 characters.  Our Datum controllers immediately looked for a CRC after a 2-char gap, and got a CRC/LRCC error when it hit those little gaps.  This would be on 800 BPI NRZI tapes, of course. Jon