t...@harminc.net (Tony Harminc) writes: > I assume it is the value used in the Set Sector/Read Sector CCWs. This > came with the 3330 (real "analogue" disk) and is part of Rotational > Position Sensing (RPS). It should have no logical relationship to the > cell size; it's just a logical position (degrees, radians, IBM magic > numbers because degrees and radians were NIH...?) on the track.
re: http://www.garlic.com/~lynn/2018.html#77 CKD details it use to be all surfaces were data ... with the 3330, one surface became dedicated to the sector position ... 20 r/w heads, 20 surfaces, 19 data r/w heads, 19 data surfaces ... the 20th surface has the rotational position information recorded. Supposedly the loss in total data capacity was more than offset in better system throughput ... RPS "set sector" in channel program reducing channel busy involved in constant search (although it couldn't fix multi-track search for VTOCs and PDS directorys). All that goes away in FBA ... as can be seen in justification description going from 512 FBA to 4096 FBA: https://en.wikipedia.org/wiki/Advanced_Format i've periodically mentioned pointing out that in the 70s, increase in disk throughput wasn't keeping up with increase in overall system performance. Some disk division executive in the early 80s took exception with my statement that relative system disk throughput had declined by an order of magnitude since the 60s (disk throughput increase 3-5 times, processor&memory throughput increase 40-50 times) and assigned the division performance group to refute my claim. After a couple weeks the group comes back and essentially say that I had slightly understated the problem ... not bothering to include RPS-miss in the calculations (attempting to channel reconnect at the sector number ... but channel busy with some other device ... and so have to loose full revolution). They then turn the analysis into SHARE presentation on how to organize disk farms for better throughput. -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
