mwandel@tiger.waterloo.edu (Markus Wandel) (02/27/90)
Original-posting-by: mwandel@tiger.waterloo.edu (Markus Wandel) Original-subject: Re: Performance Rating w/ A2091 and Quantum ProDrive 40S Reposted-by: emv@math.lsa.umich.edu (Edward Vielmetti) I tried replying via mail, but the reply bounced, so I'm posting this... In article <22452@uflorida.cis.ufl.EDU> jma@beach.cis.ufl.edu (John 'Vlad' Adams) writes: > > ... > > The Quantum is rated at 2.0 megabytes/second asynchronious transfer > rate in addition to having a 64k cache. So I doubt the drive slows > the performance. So is this standard? Has Commodore limited a > speed demon? > > ... No way a Quantum disk will actually give you 2.0 Megabytes/sec sustained data transfer. This is only the speed rating for its SCSI bus interface, using the asynchronous protocol. It does not account for delays between bursts of data from the drive. You can easily work out the theoretical maximum data transfer rate from your disk's specs, if you have them. For mine, for example: 3600 RPM 27 sectors/track 512 bytes/sector That's 60 revolutions per second at 27*512 bytes readable by one head during one revolution, for an absolute theoretical limit of 829,440 bytes/sec. Many factors detract from this, to the point where I believe the maximum transfer rate possible with this disk is about 500-600 K/sec. I've never seen a Quantum giving more than 650K/sec, so I believe its useable transfer rate is in that area. Some disks come with a claimed "sustained average transfer rate" -- something I would interpret to mean the speed at which you can actually get data from the disk. But for both the SCSI disks I have, it is given incorrectly at something well exceeding the theoretical rate at which data can be read in the first place. I've also found that a 68000 based Amiga doesn't really need more than 300K/sec disk transfer rate. My (homemade) interface goes that fast, and I've found that all my compiles, Zoo compresses, etc. are now compute bound as shown by the low duty cycle of the "blips" of the disk activity light. And my interface isn't even DMA. So don't worry about it... Markus Wandel mwandel@tiger.waterloo.edu (519) 884-9547