Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: "Stephen Fuld" Newsgroups: comp.arch Subject: Re: Architectural implications of locate mode I/O Date: Sat, 6 Jul 2024 06:15:56 -0000 (UTC) Organization: A noiseless patient Spider Lines: 30 Message-ID: References: <1bed88y8na.fsf@pfeifferfamily.net> <87frsnwbd5.fsf@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit Injection-Date: Sat, 06 Jul 2024 08:15:56 +0200 (CEST) Injection-Info: dont-email.me; posting-host="5a5b4a14ad108e87257501bec18daf2b"; logging-data="3899135"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19TuWWnPLc3q8nshElmoaiY+VkBj1X7zrI=" User-Agent: XanaNews/1.21-f3fb89f (x86; Portable ISpell) Cancel-Lock: sha1:CpF9/Qm0kywrsImaNWUOv2xddU4= Bytes: 2409 Lynn Wheeler wrote: > John Levine writes: > > By putting most of the logic into the printer controller, the 1403 > > was not just faster, but only took a small fraction of the CPU so > > the whole system could do more work to keep the printer printing. > > 360 "CKD DASD" and multi-track search trade-off. As you posted below, the whole PDS search stuff could easily be a disaster. Even with moremodest sized PDSs, it was inefficient has hell. Doing a linear search, and worse yet, doing it on a device that was slower than main memory, and tying up the disk controller and channel to do it. It wasn't even sort of addressed until the early 1990s with the "fast PDS search" feature in the 3990 controller. The searches still took the same amount of elapsed time, but the key field comparison was done in the controller and it only returned status when it found a match (or end of the extent), which freed up the channel. Things would have been much better if they simply used some sort of "table of contents" or index at the start of the PDS, read it in, then did an in memory search. Even on small memory machines, if you had a small sized index block and used something like a B-tree of them, it would have been faster. -- - Stephen Fuld (e-mail address disguised to prevent spam)