joe@amos.ucsd.edu.ling.ucsd.edu (Joe) (03/11/90)
Why aren't there any dedicated-scsi chip/cards for the mac which work? The idea is simple: you have a processor with a large cache; in theory, writes to disk are handed-off instantly from the cpu to the coprocessor. If the cache is large enough, many types of reads could be nearly instantaneous as well. Why not? I understand the new, nefarious Mac IIxi will have some of this feature, but could someone enlighten me as to how all this _REALLY_ works ??? Joe. * * "Think, imagine, feel" are words like good and evil; * they mean what you choose them to mean - and nothing more. * If you define them, they fall apart. * * INTERNET: joe@amos.ucsd.edu * BITNET: joe%amos.Bitnet * * Salk Institute for Biological Research, La Jolla, Ca *
meese@vax1.acs.udel.EDU (Tim Meese) (03/12/90)
In article <7974@sdcsvax.UCSD.Edu> joe@amos.ucsd.edu.UUCP (Joe) writes: >Why aren't there any dedicated-scsi chip/cards for the mac >which work? The idea is simple: you have a processor with >a large cache; in theory, writes to disk are handed-off >instantly from the cpu to the coprocessor. If the cache is >large enough, many types of reads could be nearly instantaneous >as well. > >Why not? > >Joe. Apple will announce yet another high-priced Mac (er, workstation?) on Mar 19 called the IIfx (40 MHz 68030) which will include among other things, such as a Fast Memory Controller that will allow burst mode reads and writes to RAM, a I/O chip called an IOP. The IOP will have a 6502 microprocessor and a 32KB buffer to relieve the '030 of I/O to the floppy disks and ADB, as well as LocalTalk network I/O. The report I read didn't mention anything about intercepting SCSI I/O, but I would imagine that might be the next data stream Apples engineers may work on. Tim -- Tim Meese \\\\ Internet: meese@vax1.acs.udel.edu Electrical Engineering Department //// UUCP: ...!udel!udccvax1!meese University of Delaware \\\\ Voice: (302) 475-8756
ts@cup.portal.com (Tim W Smith) (03/18/90)
There are several reasons why there are no SCSI caches/accelerators for the Mac that work. 1. The NuBus interface on the Mac II is *SLOW*. 2. The Mac II SCSI Manager is faster than most hard disks 3. The time spent transferring data is small compared to the time it takes the disk to find the data. 4. The cache available in the control panel is pretty good. A third party cache does not help this much. The new Mac with DMA for SCSI might help performance, because it won't have to go through the NuBus. Tim Smith