Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!caen!uwm.edu!bionet!agate!pasteur!dog.ee.lbl.gov!nosc!ucsd!mvb.saic.com!ncr-sd!se-sd!cns!dltaylor From: dltaylor@cns.SanDiego.NCR.COM (Dan Taylor) Newsgroups: comp.sys.amiga.hardware Subject: Re: SCSI-1 vs. SCSI-2 Message-ID: <869@cns.SanDiego.NCR.COM> Date: 16 Mar 91 02:47:40 GMT References: <1991Mar8.200331.5111@javelin.es.com> <1991Mar11.163108.12361@hollie.rdg.dec.com> <6034@bwdls58.bnr.ca> Organization: NCR Corp. SE-San Diego Lines: 36 In <6034@bwdls58.bnr.ca> dwjz@bcarh660.BNR.CA (Doug Zolmer) writes: >For the added expense, SCSI-2 will not give any marked advantages over regular >SCSI in the average personal computer. Not strictly true. If you have multiple SCSI-attached devices, such as laser printers, tape drives, network interfaces, or multiple disks, then properly designed SCSI-2 (fast or wide, or both) devices with caching, or at least, large buffers, will show noticeable performance increases. I did see the word "average", though. Since the "average" (SCSI-equipped) personal computer is a plain, old, dumb, slow Mac, you're right. But this question really was asked about the A3000, hardly an "average" personal computer. SCSI-2 would be an asset, there. Even the newer Macs, if they had it, and EISA PCs, some of which do, will show a performance with SCSI-2. The real advantage of the higher transfer bandwidth is the ability to move large blocks between buffers/caches on the disk, etc. and similar buffers/caches on the host, without hanging up the requesting process for a lot longer than necessary. At 800Kb/s, a typical 512 byte block of data takes 640usec of data transfer, while at 4Mb/s, I can move 2048 bytes in 512usec. If the 2Kb is cached locally, then we never have to go through the request phase of the SCSI bus for the other 3 512 byte blocks, which is a real savings, since the first block didn't take any longer to arrive with SCSI-2, than -1. Remember, our Amigas are multitasking, we often have several SCSI transactions pending. Faster transfers allow closer interleaving of transactions, again a savings. The extra cost would be noticeable on an A500/A590 class machine, but in my 2500/30, or an A3000, particulary with multiple drives, the added cost would be negligible. Dan Taylor * My opinions, not the companies.