Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!cps3xx!eecae!abaa!esker From: esker@abaa.uucp (Lawrence Esker) Newsgroups: comp.sys.amiga Subject: Re: Questions about Harddisks Message-ID: <5182@abaa.UUCP> Date: 30 Nov 89 16:29:06 GMT References: <553@bmers58.UUCP> <32033@watmath.waterloo.edu> Reply-To: esker@abaa.UUCP (Lawrence Esker) Organization: Allen Bradley Lines: 56 >In article <553@bmers58.UUCP> keithh@atreus.UUCP (Keith Hanlan) writes: >>o DMA vs non-DMA >> I'm almost ready to give up. I continue to read conflicting >> optinions about DMA vs non-DMA hard-disk controllers. My gut >> opinion is that DMA is a more elegant solution that off-loads the >> CPU and hence doesn't degrade the machine as much. Am I right? Yes. >> Then why does anybody build non-DMA? Faster time to market in design. No benifit to the consumer (IMHO). A non-DMA board just looks like a memory board (if buffer ram) or an I/O port (if FIFO based) via the computer bus. >> Why do they claim such remarkable through-put with some non-DMA drives? Because the predominante speed factor with drives is the seek and access time. The difference in buffer passing is a small percentage of this, so the user doesn't usually notice. However, load down the system in a multitasking Amiga, and that small percentage turns into a large one. As I've mentioned before, a non-DMA slows down for ANY other tasks that may be running. A DMA device slows down only if that other tasks is using overscan hi-res graphics. (Although that no excuss for the A2090 problems.) In article <32033@watmath.waterloo.edu> himacdonald@grand.waterloo.edu (Hamish Macdonald) writes: >In effect you are correct. They sell non-DMA controllers because people >will buy them... and because they are cheaper to build/buy. Anytime I have compared prices, the non-DMA have been close enough to the same price as DMA to not make a difference. They may be cheaper to build, but not buy (ie. more profit). From a hardware designers's viewpoint, I don't believe much in the cheaper to build area either. They require so much more buffer ram and glue logic that its price overcomes the savings for a simple DMA chip. >> And finally, what the heck is the "quasi" DMA and "true" DMA I occassionally >> hear about. >>Keith Hanlan >Don't know about 'quasi' DMA. Quasi-DMA is a marketing buzzword I head from some non-DMA people (I think it GVP). The non-DMA boards have circuitry that directly dumps the data into the onboard buffer ram, which is what DMA is by definition. Its just that it is DMA into the buffer ram using simple glue logic instead of into the system memory by a complex DMA controller chip. >Hamish. -- ---------- Lawrence W. Esker ---------- Modern Amish: Thou shalt not need any \ * * * ******* / computer that is not IBM compatible. \ * * * * * / \ * * * * * ***** / Sr. Hardware/ASIC Design Engineer \ * * * * * * / Allen-Bradley Communications Div. \ ******* * * ******* / Work: (313)668-2500 Home: (313)973-8561 ----------------------------- Compuserve: 76337,2524 UseNet Path: __!mailrus!sharkey!itivax!abaa!esker == esker@abaa.UUCP