<U35832@uicvm.uic.edu> (04/12/91)
I understand there is the EISA architecture and the regular arch. For 486's what would be the best to consider? Which is the best architecture? What the hell is the difference? Shawn University of Illinois at Chicago P.S. Which one has the best future? (Which one will outlast the other, in the long run?)
andrewsh@lonex.radc.af.mil (Harold G. Andrews II) (04/13/91)
In article <91101.194645U35832@uicvm.uic.edu> U35832@uicvm.uic.edu writes: >I understand there is the EISA architecture and the regular arch. >For 486's what would be the best to consider? > That really depends on what you are doing and how much more you are willing to pay for EISA boards vs ISA boards. Right now, the availibility of EISA boards is limited, and those that are available are more than just slightly expensive. For instance, Mylex sells three EISA boards (not including their EISA mother boards) that, performance-wise, do things no ISA board can hope to accomplish in the near future. They are the only company I am aware of currently marketing EISA boards. >Which is the best architecture? > This rather depends on you definition of "best". If flexibity is your thing then the EISA architecture is probably the way to go. You may want to do some kind of cost-benefit analysis to see if you really need the increased performance and flexibility the EISA architecture offers over the older ISA architecture. >What the hell is the difference? > The history as I understand it: When IBM first came out with their PC way back when (circa 1981 I believe) they had an 8-bit bus. When they decided to come out with an 80286 based machine (the IBM PC/AT) they decided to upgrade the bus to accept 16 bit cards as well as the older 8 bit cards. Thus was born ISA (the Industry Standard Architecture). This downward compatibility was one of IBM's major selling points for the AT's (this did not come without its problems, however). By this time, though IBM had some competition. Compaq and others were coming out with lower priced machines with better performance, more features etc. IBM then figured it had had enough of its competitors meddling in the market, and decided to throw a monkey wrench into the market. The impression I get is that upper management at IBM felt that they had been successful thus far in directing where the market went. After all, their 8086 machines had become an instant standard. IBM designed a new architecture, called the micro-channel architecture (or MCA) which had a 32 bit bus. The catch was that this new architecture was not downwardly compatible with the existing 16-bit ISA. In response to this, a consortium of several companies (Compaq, Hewlett-Packard, Tandy and four others that I forget) got together to design a 32 bit downwardly compatible bus architecture which has become known as EISA (the extended industry standard architecture). Now, EISA will allow you to use the older 16 bit cards, the even older 8 bit cards (if you can find them any more) and the new 32 EISA cards. You probably won't notice any improvement in performance using the 16 bit cards in an EISA slot (though I could be mistaken). You will, however, see a sizable increase in the speed with EISA cards in EISA slots (as opposed to an ISA card in an EISA slot with the same "purpose in life" as the EISA card in question). > >Shawn >University of Illinois at Chicago > > >P.S. Which one has the best future? (Which one will outlast the other, >in the long run?) > I don't know. I can't see into the future. At a guess, I would believe that the EISA bus, being the next logical progression in this bus architecture evolution, would probably outlive the older ISA architecture. Others will disagree. It's a matter of who you ask. -Andy ******************************************************************************* * Harold G. "Andy" Andrews II * "Many the man whose punctuality * * andrewsh@lonex.radc.af.mil * serves only to warm his chair." * * Rome Laboratory/IRRE * * * Griffiss AFB, NY 13441-5700 * - M. Kabrisky * * (315) 330-7788 (DSN Prfx 587) * (Not an official USAF viewpoint) * *******************************************************************************
mattij@tuura.UUCP (Matti Joutkoski) (04/18/91)
andrewsh@lonex.radc.af.mil (Harold G. Andrews II) writes: >them any more) and the new 32 EISA cards. You probably won't notice any >improvement in performance using the 16 bit cards in an EISA slot (though I >could be mistaken). You will, however, see a sizable increase in the speed >with EISA cards in EISA slots (as opposed to an ISA card in an EISA slot >with the same "purpose in life" as the EISA card in question). Basic improvements of EISA are: 32-bit bus 33 Mhz Level trigged interrupts Bus-mastering Level trigged interrupt allows, that the same interrupt can be shared for a many different cards (if nesseccery). How it happens, is i.e. two cards will give interrupt at the same time. All right, EBC (EISA Buss Controller) will scan all those slot-specified I/O addresses, that 'was it you, who wanted a interrupt' and gives it. If the interrupt is still asked, then EBC will again scan those I/O addresses, that who has been without IRQ. So we have extra I/O addresses for every slot/card. And we don't have more IRQs than ISA bus has. But EISA (only EISA) cards can share them, so it will not be a problem. Bus mastering is not anymore DMA-based like in old ISA-machines. Now it is truth busa-mastering. It will help a lot, that the card can do lots f work without loading the CPU. Then we have ofcourse PS/2 styling configuration system for all EISA- cards. SO the configuration of EISA (ISA cards can be used, but not needed to be configured) cards is stored in the PC, and the BIOS will check in every boot, is that information correct. Normaly those EISA- cards are a little bit smarter, so we don't need to chance any jumpers to chance the IRQ, DMA aso. You can do it by EISA-configuration prg. About the future of EISA. I would say that it is very good, if we are thinking about the future. The I/O will not be the bottleneck for a years. Harddisks and memory are now adays. I have used the Mylex EISA SCSI-controller under a Unix, and I have to say it is lovely. Mostly it is because of cache, but busmastering and EISA makes wonder- full things. What do we do by the fast cache, if our DMA maximum speed is 8 Mhz? Nothing. -- --------------------------------------------------------------- Matti Joutkoski, mattij@yj.data.nokia.fi, tel. + 358-0-5673866. ---------------------------------------------------------------