9 track tapes and block sizes

Jon Elson elson at pico-systems.com
Mon Oct 5 10:50:42 CDT 2020

On 10/04/2020 11:30 PM, Chuck Guzis via cctalk wrote:
> The problem arose if the program either failed to keep up 
> (e.g. competing programs demanding the CPU) or if an ECS 
> transfer occurred. Where I got involved was with a 4-CPU 
> configuration sharing 4MW of ECS, using the ECS for swap 
> space. ECS transfers completely swamp the read/write 
> pyramid, so the PP gets locked out and can't service the 
> drive. Recovery was doing a backward-read to the BOT or 
> preceding IRG. Lather, rinse, repeat. It was fun to watch 
> and we never solved that one to anyone's satisfaction.
I can't imagine any way to fix this except to put a buffer 
memory in the PP big enough to hold a few records of tape 
data.  Probably played hob with disk transfers, too, except 
that wasn't as visible.


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