Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!jesup From: jesup@cbmvax.commodore.com (Randell Jesup) Newsgroups: comp.sys.amiga.hardware Subject: Re: SCSI-1 vs. SCSI-2 Message-ID: <19967@cbmvax.commodore.com> Date: 19 Mar 91 02:02:44 GMT References: <1991Mar8.200331.5111@javelin.es.com> <19745@cbmvax.commodore.com> <2216@wet.UUCP> <19941@cbmvax.commodore.com> Reply-To: jesup@cbmvax.commodore.com (Randell Jesup) Organization: Commodore, West Chester, PA Lines: 39 In article <19941@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes: >In article <2216@wet.UUCP> pk@wet.UUCP (Philip King) writes: > >>Dave, does this mean that Amiga hard disk controllers support synchronous >>transfers? I don't think I've ever seen any of the host adaptor >>manufacturers claim that. > >Sure do. Apparently, though, the our host adaptors won't normally request >synchronous transfers. Some drives lock up, or otherwise misbehave, if you >ask for synchronous transfers. Yup. We will do synchronous if the drive requests it (quantums can be told to request it: mode select page 55, byte 2, bits 4 and 5). There may be a battmem bit for it; ask steve. Some older scsi drive (guess who) will crash and take the bus down with them if asked to do synchronous. >Chances are, going to synchronous mode won't result in much of a speedup >anyway in a single drive system. In most cases, the drive is the limiting >factor, not the SCSI bus. It might make a visible difference on high end >drives with large caches. Randell or Steve may have looked at this question >in greater detail. Also correct. Without synchronous, my Quantum 210S gets 1.2M/s max. With it, I get 1.2M/s max. The win to synchronous is when you have multiple drives in use: a given drive stays on the bus less. It can also be a win when you get a cache/preread hit in the drive cache. These things do not usually show up in disk speed test, but might when running compiles on two drives at the same time, for example. The big limiting factor is usually the speed at which bits come off the platters. The new CDC/Seagate ST1480, for example, spins at 4400 rpm and can do 1.7M/s through the FS. -- Randell Jesup, Keeper of AmigaDos, Commodore Engineering. {uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com BIX: rjesup The compiler runs Like a swift-flowing river I wait in silence. (From "The Zen of Programming") ;-)