Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: Hard disk transfer rates Keywords: Big, mean, fast & shiny controllers Message-ID: <14418@cbmvax.commodore.com> Date: 13 Sep 90 20:17:52 GMT References: <3769@ruuinf.cs.ruu.nl> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 62 In article <3769@ruuinf.cs.ruu.nl> ttavolij@praxis.cs.ruu.nl (Thomas Tavoly) writes: >In article <14330@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave >Haynie) writes: >>Typical SCSI devices use the asynchronous transfer mechanism, which is limited >>to about 1.5 MegaBYTES per second. Synchronous SCSI, which uses a clock >>rather than a handshake to clock its data, runs at a peak of 4-5 MegaBYTES >>per second. Currently, you won't find actual disk drives that can get data >>off their platters much faster than the 1.5 MegaBYTES per second of the >>asynchronous SCSI, and most are slower. >1. Actually I read something about the IVS Trumpcard Professional version >which will achieve a transfer rate of 1.8 MBytes/sec. That's not bloody likely. You figure any no wait state cycle on the A2000 takes 560ns. Discounting the overhead of the copying loop itself, you need memory two cycles to transfer 16 bits, so you're capable of transferring 1 byte every 560ns. So it'll take 587,202,560ns to transfer a megabyte. Which is 1 Megabyte every 0.5872 seconds, or about 1.703 Megabytes/second. So, without DMA, you can't possibly get stuff off a hard disk any faster than that across the A2000 bus, and anyone who says differenly is lying to you. And in reality, it's slower than that, since the CPU needs to fetch instructions (you probably get close to this speed with a 68010 using loop mode for the transfer). Of course, none of this is going to tell you how fast the transfer or the effective disk speed is going to be. The speed of SCSI, if asynchronous, will be another limiting factor. The actual speed of the hard disk still another. >Rumour has it that this card will be out soon (what? Maybe 1992? ;-). To get close to those speeds with that card, you would need to have a synchronous SCSI interface going at 2 megabytes/second or so, and you would also need a SCSI device capable of actually supplying data that fast. This also implys, in a non-DMA device, that the device is parasitic -- it waits on the SCSI bus for data, to get it over as fast as possible, rather than buffering at SCSI speeds and transferring full speed once SCSI is done. >Is this with a stock 68k Amiga or some '030? A 68030 system with a non-DMA controller can get faster transfers across the A2000 bus. For example, while the A2630 can run a 560ns cycle out to the Zorro II bus, it can manage a 200ns cycle, at 32 bits wide, to it's own memory. So in theory, you could achieve a rate of 1 byte every 330ns, or 2.89 megabytes/second, though with synchronization delays considered, it'll be something less than this. With DMA, the theoretical limit on the A2000 is 3.41 megabytes/second. >I believe that the method employed here is using a 16 bit wide bus (dubbed >SCSI II), instead of the former 8 bits. SCSI II isn't 16 bits wide, it's still 8 bits. It specifies the SCSI command set in a much more standardized fashion than original SCSI, and has a fast synchronous transfer mode capable of 10 megabytes/second. But it really doesn't matter what your fastest transfer rate is capable of in a system, the limit is based on the slowest element in the link, whether that be A2000 bus transfer speed, SCSI speed, or the hard disk's own speed. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Get that coffee outta my face, put a Margarita in its place!