UH2@psuvm.psu.edu (Lee Sailer) (06/06/90)
I don't know much about hardware.
I got to wondering the other day how Zorro II and III compares and contrasts
with EISA and MCA? I know that IBM tries to make out that MCA is some
wonderfully enhanced bus that nobody would want to be without. What's it
do that Zorro doesn't?
leedaveh@cbmvax.commodore.com (Dave Haynie) (06/08/90)
In article <90156.130512UH2@psuvm.psu.edu> UH2@psuvm.psu.edu (Lee Sailer) writes: >I got to wondering the other day how Zorro II and III compares and contrasts >with EISA and MCA? I know that IBM tries to make out that MCA is some >wonderfully enhanced bus that nobody would want to be without. What's it >do that Zorro doesn't? Not much. The big news with EISA or MCA are what they do that the PC bus doesn't ordinarily do. With the PC-AT bus (sometimes called ISA bus), you set a bunch of jumpers on a card to determine where in the memory map it goes. The bus has interrupts, but they can't be shared between cards, so it's quite possible to run out of interrupts. And cards can't normally be bus masters -- the only DMA facility is with a DMA controller on board, which is actually slower than using the CPU in fast AT style systems. EISA and MCA do it differently, but they have much the same basic ideas. Each has some way for software to recognize a card and locate it without the use of jumpers. I've heard the MCA method described as "just as difficult as the PC-AT, only the jumpers are software now instead of hardware", but I've never used an MCA system myself, so I can't comment on how accurate that might be. Both systems permit shared interrupts, both allow bus masters. At least MCA has some kind of bus master priority scheme. Both systems also define some kind of burst or block memory transfer, which is often very effective when you have I/O bus masters. Both MCA and EISA permit 32 bit transfers. Zorro II has had most of these concepts since the beginning. It has always supported true bus masters, shared interrupts, and software configuration. In fact, AUTOCONFIG(TM) is a Commodore trademark. All of Commodore's hard disk controllers and those from several other companies are bus master devices; only recently have SCSI bus mastering controllers become available for MCA or EISA. Zorro III extends many of the Zorro II concepts. It provides a 32 bit wide data transfer with an optional burst memory transfer. It doesn't provide any bus master priority mechanism, but does enforce fairness between competing masters, so no master can be locked out of the bus (this fairness works for both Zorro III and Zorro II cards in a Zorro III backplane). > lee -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "I have been given the freedom to do as I see fit" -REM