Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-lcc!ames!cit-vax!amdahl!mat From: mat@amdahl.UUCP (Mike Taylor) Newsgroups: comp.periphs,comp.unix.wizards Subject: Re: Fujitsu 2361's, SC7003's, 4.3BSD Message-ID: <4956@amdahl.UUCP> Date: Sun, 4-Jan-87 21:53:52 EST Article-I.D.: amdahl.4956 Posted: Sun Jan 4 21:53:52 1987 Date-Received: Mon, 5-Jan-87 01:37:01 EST References: <6387@allegra.UUCP> <1305@cit-vax.Caltech.Edu> <4892@mimsy.UUCP> <1421@cit-vax.Caltech.Edu> Organization: Amdahl Corp, Sunnyvale CA Lines: 23 Xref: mnetor comp.periphs:95 comp.unix.wizards:496 In article <1421@cit-vax.Caltech.Edu>, mangler@cit-vax.Caltech.Edu (System Mangler) writes: > > The object of sector searching is to avoid tying up the controller > with disk rotational latency. It only gains something if another > drive is ready to do a transfer immediately. This is an unlikely > event on a low-end VAX, which doesn't have enough CPU power to > keep a Massbus controller that busy, and which can ill afford the > additional interrupts. > Sector searching was introduced (as far as I know - there may have been prior art) by IBM with the 3330 DASD in about 1970, called Rotational Position Sensing. The idea was to optimize the use of S/370 channels, rather than control units. It worked OK, but now has been enhanced to allow the reconnecting controller to select among multiple attached channels, thus improving the chances of a free channel being found when needed. Since multiple controllers will normally be attached to a channel, the controller is generally not as scarce a resource. -- Mike Taylor ...!{ihnp4,hplabs,amd,sun}!amdahl!mat [ This may not reflect my opinion, let alone anyone else's. ]