The following message is a courtesy copy of an article that has been posted to bit.listserv.ibm-main,alt.folklore.computers as well.
[email protected] (McKown, John) writes: > Does anything other than S/360 derived systems even use CKD type DASD? > PDS directories are built around CKD. And, in their day, moving the > search logic out to the peripheral was probably a good idea. basically traded-off lack of real storage (for indexes) for i/o resources (channel, controller, device) ... by the mid-70s, that trade-off had started to invert ... and multi-track searches for VTOC and PDS directories were the wrong thing. set-sector introduced in early 70s with 3330s, attempted to offset the channel/controller overhead for simple CKD searches ... but didn't help with the multi-track searches. it was also somewhat seen in the discord between IMS group and system/r (original relational/sql) in the late 70s ... IMS pointing out that the implicit relational indexes consumed a lot more hardware resources ... and system/r pointing out that it eliminated a lot of IMS administrative care&management. The increasing amounts of real storage really started to tip the balance by the mid-80s ... allowing the relational indexes to be cached. misc. past posts mentioning system/r http://www.garlic.com/~lynn/submain.html#systemr misc. past posts discussing the ckd/multi-track search trade-off changing by the mid-70s http://www.garlic.com/~lynn/submain.html#dasd in the early 80s, the MVS group gave me a cost estimate of $26m to migrate off of CKD ... even if I gave them fully tested & integrated code (i.e. just cost for documentation and training). I could only use incremental sales for ROI business case ... and the claim was that customers would just buy the same amount of non-CKD as they were buying CKD (I couldn't use long-term corporate & customer life-cycle costs of continuing with CKD, I had to show $100m-$200m incremental sales). -- 42yrs virtualization experience (since Jan68), online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
