Path: csiph.com!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Lynn Wheeler Newsgroups: comp.arch Subject: Re: Is Parallel Programming Hard, And, If So, What Can You Do About It? Date: Mon, 26 May 2025 15:36:22 -1000 Organization: Wheeler&Wheeler Lines: 43 Message-ID: <87ldqi6dih.fsf@localhost> References: <0ec5d195f4732e6c92da77b7e2fa986d@www.novabbs.org> <2025May13.094035@mips.complang.tuwien.ac.at> <100oetb$c5c7$1@paganini.bofh.team> <100q47d$3k7s2$1@dont-email.me> <100srqk$pos5$1@dont-email.me> <100vm4s$16av3$1@paganini.bofh.team> <100vq44$1h5c4$1@dont-email.me> <1010910$1k3iu$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain Injection-Date: Tue, 27 May 2025 03:36:25 +0200 (CEST) Injection-Info: dont-email.me; posting-host="7d0b6b0a9a9e3bac7f27b47da3049475"; logging-data="2403667"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19E6t8ZAl02QuwnFKTVnqceNyWwH6VfDFo=" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:WUZ/A9T+G3aJnG5Hf2Z6WdKg85U= sha1:AhAj92UchzReG3jNJJPJBDwE++c= Xref: csiph.com comp.arch:111845 Stephen Fuld writes: > Yup. And IIRC the IBM 3380 had a linear actuator with two heads per > arm, one covering the outer cylinders, the other the inner > cylinders. The tradeoff was shorter seeks, thus smaller seek time but > higher cost due to more heads. original 3380 had 20 track spacings per data track, they then cut the spacing in half, doubling number of tracks per platter (and double the capacity), then cut it again for triple the number of tracks per platter (and triple capacity). doing some analysis moving data from 3350s to 3380s ... avg 3350 accesses per second divided by drive megabytes ... for avg access/sec/mbyte. 3380 mbytes increased significantly more than avg. access/sec ... could move all 3350 data to much smaller number of 3380s but with much worse performance/throughput. at customer user group get-togethers there were discussions about how to convince bean counters that performance/throughput sensitive data needed to have much higher accesses/sec/mbyte. Eventually IBM offers a 3380 with the 1/3 data track spacing as the original 3380, but only enabled for the same number of tracks as the original 3380 (as a high performance/throughput drive, since head only had to travel 1/3rd as far). other trivia: 2301 fixed head drum was effectively same as 2303 fixed head drum, but transferred four heads in parallel, 1/4 the number of tracks, tracks four times larger and four times the transfer rate (still same avg. rotational delay). late 60s, 2305 fixed head disk first appeared with 360/85 and block mux channels. There were two models, one with single head per track and one with pairs of heads per data track, half the number of data tracks and half the total capacity (same number of total heads). The were offset 180 degrees, and would transfer from both heads concurrently for double the data rate with a quarter avg rotational delay (instead half avg rotational delay), 2305 http://www.bitsavers.org/pdf/ibm/2835/GA26-1589-5_2835_2305_Reference_Oct83.pdf -- virtualization experience starting Jan1968, online at home since Mar1970