Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!pt.cs.cmu.edu!sei.cmu.edu!netnews From: netnews@sei.cmu.edu (Netnews) Newsgroups: net.arch Subject: discs with variable density Message-ID: <387@aw.sei.cmu.edu.sei.cmu.edu> Date: Thu, 6-Nov-86 08:32:13 EST Article-I.D.: aw.387 Posted: Thu Nov 6 08:32:13 1986 Date-Received: Fri, 7-Nov-86 09:18:41 EST References: <1128@tekig5.UUCP> <5100141@ccvaxa> <553@cubsvax.UUCP> <2474@peora.UUCP> <1256@hoptoad.uucp> Reply-To: firth@bd.sei.cmu.edu.UUCP (PUT YOUR NAME HERE) Organization: Carnegie-Mellon University, SEI, Pgh, Pa Lines: 25 Keywords: variable disc density The discs on the English Electric KDF9 spun at constant speed but had a variable number of sectors per track. The gory details: From: firth@sei.cmu.edu (Robert Firth) Path: sei.cmu.edu!firth speed: 1000 rpm discs: 16 (+ 2 for control) read arms: each arm had 4 heads above and 4 below the platter, and could be moved to 64 positions, giving 256 tracks per surface or 512 per disc. blocking: The inner half of each surface had 8 sectors per track and the outer half had 16; each sector was 40 words and each word was 48 bits. Total capacity was therefore about 3.9 Mword. Transfer rate was 10600 word/sec for the outer zone and half that for the inner zone; average latency was about 240ms. It was a beast to program, too!