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Newsgroups: comp.os.386bsd.questions Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!cnn.nas.nasa.gov!wilbur.nas.nasa.gov!tweten From: tweten@wilbur.nas.nasa.gov (Dave Tweten) Subject: Re: ISA or EISA ? Message-ID: <CD9MMF.5wA@nas.nasa.gov> Sender: news@nas.nasa.gov (News Administrator) Nntp-Posting-Host: wilbur.nas.nasa.gov Organization: NAS Systems Division, NASA Ames References: <CD8wJM.7n8@latcs1.lat.oz.au> Date: Sun, 12 Sep 1993 23:59:02 GMT Lines: 99 In article <CD8wJM.7n8@latcs1.lat.oz.au> wongm@latcs1.lat.oz.au (M.C. Wong) writes: > However, having chatted to my vendor (of my existing ISA machine), I >was told that EISA + VLB slots board does not exist, and EISA is going to >face extinction soon! Clearly a vendor who doesn't sell what you want, tring to get you to want what he sells. The AMI Enterprise III board in the machine I'm using now is only one of such "non-existent" board models. There are several others. >To my impression, it >seems as if EISA is more likely to be the trend over ISA, who is right, >me or my vendor ? EISA is clearly on the upswing, but it is still a minority product, primarily because it is still more expensive. The ISA market is dominated by the cheap no-name clones. Your vendor can sell them cheaply, and still make a nice margin. >Secondly, my vendor claimed that for EISA and ISA, the performance of >Ethernet card is unlikely to make an observable difference, since the >peak transfer rate is 10Mbits/sec! Depending upon your operating system, he may be right. If you use MS-DOS, Windows 3.1 or some other one-task-at-a-time operating system, one I/O operation at a time gets access to your I/O bus and the CPU waits for it. ISA DMA can get 4 megabytes per second or so out of the bus. A really fast ISA bus master can do 8 megabytes per second, max. EISA is capable of about 32 megabytes per second. But the ethernet is only capable of about 1 megabyte per second. DOS will wait about the same time for either an ISA or an EISA ethernet card -- a time determined by the ethernet. All this changes if you want to run a true multiprogramming operating system, like, oh, say 386bsd. A bus-mastering EISA ethernet card will use about 1/32 the theoretical bandwidth of the I/O bus, max. A 16-bit ISA bus mastering ethernet card will use about 1/8, max. A 16-bit DMA ISA ethernet will use about 1/4, max. If you're doing anything else (like putting all those ethernet bytes somewhere) you'll notice the load much sooner on ISA. If you like lots of memory (a good thing for a multiprogramming operating system) ISA has a gocha for you too. ISA DMA and bus masters can only control 24 bits of address. That translates into a need to do all DMA and bus master transfers into and out of the first 16 megabytes of memory. Your software will have to do a memory-to-memory transfer if you have more memory than that. Lots of software packages don't oblige. >Also, he claimed that HDD transfer rate depends mainly on the controller >instead of the type of bus ! That depends upon how fast your disks are. Most PC market disks move data much more slowly than the ISA 4 megabyte per second DMA limit. Some SCSI-II drives can exceed it. None exceed the ISA bus master limit of 8 megabytes per second. It's always true that performance is determined by the slowest participant, so a bad controller could slow you down. Again, if you have a multiprogramming operating system so you're trying to service multiple I/O devices at once (say, both ethernet and disk), you will notice the difference -- if you have high performance I/O devices and controllers. >Finally, he said the different components prices >for EISA is going to be more expensive than an ISA one, and does not worth >the extra dollars! He's right about EISA expense being greater. Whether it's worth it is up to you and your application. >For myself, I would like to know for 386bsd/FreeBSD/NetBSD Unix box, >does EISA show much difference over ISA ? Yes it does. The most obvious difference isn't the speed though it is there; its the 16 megabyte gocha boundary for ISA DMA and bus masters. >And with EISA, will it promise >greater trnafer rate for Ethernet card, and how about SCSI-2 HDD, is that >affected by the type of bus (since it is DMA) ? If you choose the ISA route, get a SCSI-II HBA that uses bus mastering, not DMA. Bus mastering can move data at twice the DMA rate. While an ISA ethernet card needn't be any slower than an EISA ethernet card (particularly in a dedicated file-transfer test to /dev/null), EISA everywhere will give you more I/O bandwidth for multiprogramming. You've been phrasing your questions on the assumption that both ethernet and SCSI will be on the ISA bus. Motherboards which have VLB usually have two VLB slots. You could put a VLB SCSI HBA in the one you don't use for a graphics card. That would ease the ISA bandwidth crunch. My wallet and I voted for maximum multiprogramming bandwidth, coupled with highest performance graphics -- and that's EISA/VLB. -- --------------------------------------------------------------------------- Dave Tweten tweten@nas.nasa.gov NASA Ames Research Center, M/S 258-5 (415) 604-4416 Moffett Field, CA 94035-1000 FAX: (415) 604-4377