On 28 February 2010 16:13, Anne & Lynn Wheeler <l...@garlic.com> wrote:
> they took the 158 integrated channel microcode and split it into > separate (dedicated 158 engine) box for the 303x channel controller. > > the 3031 then becomes a 158 with just the 370 microcode and a > 2nd/separate 158 with just the integrated channel microcode In light of your oft-posted anecdotes about disk test-cell and MTTF of MVS I/O subsystem... Around 1977, a grad student friend of mine got a gig with the university to build a buffer for the unbuffered 2501 card reader, so that multiple such readers could be used over 2944 channel extenders, which added an unacceptable delay when used over close to a mile of twisted-pairs, and provoked channel overruns. (The other choice was an OEM buffered card reader, which worked fine electrically, but couldn't come close to the mechanical reliability and ability to read a warped and sticky student deck.) He did initial testing with my assistance (as sysprog and writer of standalone test programs) on our 165 or 155, depending on which was available overnight or weekends. Early debugging on the 165 (2870 byte multiplexor channel) generally resulted in appropriate I/O status codes if the interface timing was bad. The same debugging on the 155 invariably produced red lights and complete machine lockup, resolved only by power off/on. I don't know how similar the 158 and 155 really were (certainly very different front panel implementations), but it's interesting that the 303x got the microcoded channels, rather than the clunky but rock solid 28x0 hardwired ones. Tony H. ---------------------------------------------------------------------- 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
