Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!unisoft!hoptoad!wet!pk From: pk@wet.UUCP (Philip King) Newsgroups: comp.sys.amiga.hardware Subject: Re: SCSI-1 vs. SCSI-2 Message-ID: <2216@wet.UUCP> Date: 14 Mar 91 08:53:30 GMT References: <1991Mar8.200331.5111@javelin.es.com> <19745@cbmvax.commodore.com> Organization: Wetware Diversions, San Francisco Lines: 50 In article <19745@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes: [...] >There are several SCSI-1 transfer modes. Every SCSI-1 controller implements >the standard asynchronous mode, which goes around 1.5 MB/s. Some have an >improved asynchronous mode which goes 2.5 MB/s; I don't know much about it, >other than the SCSI chip used in A3000 and A2091 supports this. Then there's >the synchronous mode, which, depending on the clock used, runs up to about >5 MB/s (I think the A3000 runs it at around 4 MB/s). SCSI-2 adds a high speed >synchronous mode, which kicks up to a maximum of around 10 MB/s. If you could >find a 32 bit SCSI-2 drive, you could expect a theoretical maximum transfer >rate of 40 MB/s. > >Now, none of these transfer rates really attack the question of drive speed. >Good SCSI drives manage bursts of 1.25-1.50 MB/s, straight from the disk. >Until any seeking is necessary. The higher transfer rates help when you have >multiple devices on the SCSI bus, and also to a degree with many of the modern >drives which, like the Quantum series, have some on-drive caching and won't >always need to burst data straight from the disk. But you don't expect in a >single drive system to double your effective disk performance going from >asynchronous to synchronous or from synchronous to high speed synchronous >transfers. > 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. I happen to have a drive that supports this, and I wouldn't at all mind if I could speed it up! It's the Seagate/Imprimis ST-1239N/94350-230S model, 200MB 15ms. Apparently it's got an onboard cache memory like the Quantums, but it doesn't default to 'on' mode. Someone told me that there might be a way to activate it, if you could talk directly to it with some kind of program that issues SCSI commands. Any insight on how I might achieve that? Thanks in advance... Philip King pk@wet.uucp {ucsfcca,hoptoad,well}!wet!pk (My usenet site forces me to use more text in the followup than the text from the original article...and I already cut the heck out of it! Sheesh, it's kinda ridiculous to have to put a bunch of useless drivel at the end of my post, but otherwise it dumps me out of postnews and I have to start from scratch again! Ugh!