IBM 360 channel buttignments 523
byte multiplexor typically were unit record or telecommunication controllers. byte multiplexor could interleave multiple concurrent streams simultaneously.
IBM 360 channel buttignments 524
Rob Warnock small-but-useful byte better to this for 3380 drives, they introduced data streaming. selector & byte multiplexor had bus&tag syncronous hand-shake on every byte ... that...
when we were doing the telecommunication clone controller
one of the first bugs testing hardware on 360-67 was locking out the high-speed timer. 360-67 had high-speed timer option that updating storage location 80 (x'50'). if channel continuously locked out the memory bus so that the timer had a second tic happen before it had a chance to update memory for previous tic.
360 had byte multiplexor and selector channels. block multiplexor was a sort of interleave selector channel introduced with 370. block multiplexor allowed the 3330 "set sector" feature to suspend channel program processing until the controller raised reconnect.
Software for IBM 36030 was DOS360: Forty years 526
You're thinking of the 7330-2415 designs. The 729, 240x, and 34xx drives diffrentiated between REW and RUN only in what happened when the load point was reached; rewind speed...
in 360 ... there was paradigm that you could effectively trade off lots of i-o channel capacity for processor real storage ... dasd-disk channel program would position the arm and then search for specific record identification.
these searches would tie-up up the selector channel, controller, and device. 3330 had 19 data tracks and a 20th hardware positioning track (sector). if you knew approximately the rotational position of the record you needed ... you could insert a SET-SECTOR ccw in the channel program ... that would disconnect from the channel until that position rotated under the head (on track 20) .. in which case, it would raise channel reconnect.
by the mid-70s, the trade-off was beginning to switch with much more abundant real storage and more constrained i-o capacity. i once was called into a large national retail customer that was experiencing unexplained severed i-o bottleneck thruput. they had multiple 168s in loosely-couple configuration with SVS. It turns out that they had a large applicaton program PDS dataset with a three (3330) cylinder library directory. Standard os support used multi-track search of the program directory to find the index pointer to specific program image on disk. multi-track search would spin until it found the correct record ... or until end of cylinder (locking out the channel, controller, and device). for 3330 at 3600rpm and 19 tracks ... a full-cylinder search took appox. 300milliseconds elapsed time. On the avg. a search took 1.5 cylinders ... or about 450milliseconds ... plus time to load the program ... about .5seconds total. The whole multi-system complex was being limited to about two application program loads per second.
block multiplexor and 3330 set sector allowed for use of direct location positioning ... but os-360 had CKD multi-track search ingrained into various library and directory structures ... VTOCS, PDS, etc ... which continued to severely aggravate for years.
Software for IBM 36030 was DOS360: Forty years 525
Joe Morris i thot i usually the whole machine room to myself on the weekend ... but one weekend i got pre-empted because the ibm se and one of the univ. system...
random past references to claiming that disk relative system performance had declined by a factor of ten times over a period of years
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