Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.advocacy Subject: Re: The Amiga's Future Message-ID: <22307@cbmvax.commodore.com> Date: 10 Jun 91 18:56:06 GMT References: <1991Jun4.003619.3661@news.iastate.edu> <1991Jun4.023950.11286@ncsu.edu> <16577@darkstar.ucsc.edu> <22163@cbmvax.commodore.com> <18@ryptyde.UUCP> <1991Jun7.162105.26985@neon.Stanford.EDU> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 33 In article <1991Jun7.162105.26985@neon.Stanford.EDU> torrie@cs.stanford.edu (Evan Torrie) writes: >mykes@amiga0.SF-Bay.ORG (Mike Schwartz) writes: >>Do builtin Mac SCSI ports go at upwards of 2MB per second? > > On the IIfx, it's 3MB/s [via DMA - although because this is only >supported in A/UX, it actually ends up being slower than the IIci]. > On the IIci, it just peaks out at 1.8 - 2MB/s. > Of course, one could then ask "How many disk drives actually transfer >data at upwards of 2MB/s?" The ones which do are generally 600MB and >up drives, for which you're paying enough that it might make >sense to add in a SCSI-2 card. Well, actually, with a single SCSI device, SCSI-2 isn't going to help you any. While you might get bursts from cache faster than 10 MB/s, you're not going to get anything even approaching 5MB/s sustained from a single device. SCSI-2 is useful in a few cases, like when you have multiple drives on a bus, or some kind of RAID box. Or, in the case of the Mac-II, you're getting something even more useful along with that SCSI-II controller, a large intelligent disk cache managed by an alternate processor. Getting too concerned about real disk transfer rate is losing sight of the big picture, anyway. When the IIci is running 1.8-2MB/s, the CPU is getting no time for other tasks. When the A2000HD is running 1.8-2MB/s, the CPU is getting about 60% of it's peak CPU time. When the A3000 is running 1.8-2MB/s, the CPU is getting about 95% of it's peak CPU time (I image the Mac IIfx with DMA at the same rate would be almost as good as the A3000, assuming the DMA is full a 32 bits wide and runs full speed on its 20MHz I/O bus). -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.