The following message is a courtesy copy of an article that has been posted to bit.listserv.ibm-main,alt.folklore.computers as well.
bi...@mainstar.com (Bill Fairchild) writes: > On the REALLY old boxes (S/360), the performance problem was called a > S0C6 specification exception program interrupt and probable ABEND. > When the first S/370s were shipped in 1971, the requirement for > storage alignment was removed for most instructions, but there was a > performance hit. higher-end machines did instruction fetch a double-word at a time ... for instance, the functional characteristic manual for the 360/65 & 360/67 gave instruction timings ... which included prorated time for the double word instruction fetch ... i.e. the formula for 2-byte instruction included 1/4th of (double word) memory fetch (4-byte instruction included 1/2th of memory fetch). programmers would use cnop 0,8 in front of the start of a high-use loop ... to align it on a double word boundary ... so branch to the start of the loop would load the first 8byte of instructions in the loop ... rather than wasting time loading anything that came before the loop. 360 65 & 75 functional characteristic manuals: http://www.bitsavers.org/pdf/ibm/360/funcChar/A22-6884-3_360-65_funcChar.pdf http://www.bitsavers.org/pdf/ibm/360/funcChar/A22-6889-0_360-75_funcChar.pdf uniprocessor 360/67 was basically a 360/65 with the addition of hardware supporting virtual memory http://www.bitsavers.org/pdf/ibm/360/funcChar/A27-2719-0_360-67_funcChar.pdf multiprocessor 360/67 (described in above) was something of a different beast ... lots of differences from 360/65 multiprocessor (which was basically two independent processors sharing the same real stroage). The 360/67 multiprocessor "channel controller" allowed splitting into independent units ... but multiprocessor operation allowed for things like processors to address all available channels (more like 3081 & 370/xa). control registers were also used to "sense" the "channel controller" configuration settings (and some special models ... to also "SET" the "channel controler" configuration settings ... which not only controlled channel configuration but also memory banks). 360/67 had both 24bit & 32bit virtual addressing modes (more than 24bit addressing also didn't reappear until 3081). -- 40+yrs virtualization experience (since Jan68), online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
