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- Path: sparky!uunet!cbmvax!daveh
- From: daveh@cbmvax.commodore.com (Dave Haynie)
- Newsgroups: comp.sys.amiga.hardware
- Subject: Re: Question: Order of Bus Connections Important?
- Message-ID: <37803@cbmvax.commodore.com>
- Date: 11 Dec 92 11:58:02 GMT
- References: <23NOV199212461511@dstl86.gsfc.nasa.gov>
- Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
- Organization: Commodore, West Chester, PA
- Lines: 37
-
- In article <23NOV199212461511@dstl86.gsfc.nasa.gov> olson@dstl86.gsfc.nasa.gov (Paul Olson) writes:
-
- >I know, from having managed VAXen for the last 12 years, that the connection
- >order of peripherals to a bus is important. But I was told by a local dealer
- >that I should have my GVP SCSI upstream (i.e. closer to the CPU) of my SupraRAM
- >in my A2000 in order to improve performance. Is this true?
-
- No, the position of cards, in general, has nothing to do with performance. All
- slots on the bus run at the same speed. There can occasionally be software
- reasons for shuffling cards. For instance, a typical DMA-drive SCSI host
- adaptor on an A2000 will probably benefit if there's a memory card in a slot
- that's closer to the CPU. That's because, if the SCSI adaptor is the first
- card, there won't be any Fast RAM on the A2000, while if RAM is the first card,
- the SCSI card will be able to immediately take advantage of that Fast RAM.
- Also, you would expect combination cards to configure memory before SCSI or
- other I/O. Strangely enough, people seem more likely to put SCSI in the first
- slot and at least some combination board designs configure memory backwards.
- For the same reasons, if you knew one memory card was faster than another, you'd
- put the Fast one in first, since it would wind up first in the system memory
- list.
-
- >This seems counter-intuitive since the disk drive is slower than the RAM.
-
- The speed of a peripheral interface may have nothing to do with the speed of
- its bus interface. Accessing one card doesn't slow down other cards no matter
- which slot they're in. With Zorro II, most things are zero-wait states, so
- you don't have to worry too much. With Zorro III, you could have varying
- memory card speeds (not that anyone's plugging in multiple memory cards yet).
- The order of Zorro III I/O cards shouldn't result in any speed differences.
-
-
- --
- Dave Haynie / Commodore Technology, High-End Amiga Systems Design (cool stuff)
- "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh BIX: hazy
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