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Xref: sserve comp.unix.bsd:3709 comp.sys.ibm.pc.hardware:29202 Newsgroups: comp.unix.bsd,comp.sys.ibm.pc.hardware Path: sserve!manuel!munnari.oz.au!mips!mips!darwin.sura.net!convex!egsner!adaptex!adaptx1!neese From: neese@adaptx1.UUCP (Roy Neese) Subject: Re: Another Adaptec Question Organization: Adaptec Inc., Texas Date: Fri, 14 Aug 1992 19:21:27 GMT Message-ID: <1992Aug14.192127.13801@adaptx1.UUCP> References: <1992Aug12.193421.14456@cs.wisc.edu> Lines: 32 In article <1992Aug12.193421.14456@cs.wisc.edu> hollings@cs.wisc.edu (Jeff Hollingsworth) writes: >There seems to be two versions of the Adaptec 1542A card, one that supports bus >mastering and one that does not. I have two questions about this: > >1.) How much benefit is bus mastering for UNIX (assumming the OS supports it) > >2.) Does either BSDI or 386bsd support bus mastering? > >One other question, what exactly do the Adaptec cards do that make them >more expensive than the Future Domain cards? There are not two different versions of the 154x family. All 154x family adapters are bus masters. You may be thinking of the AHA-1522 adapter which is a non-bus master (PIO) adapter. If an adapter/controller is a bus master it just is. Software does not control this aspect of the data transfer method. Either an adapter/controller use bus mastering (first party DMA), the motherboard DMA (second party DMA), or PIO (programmed I/O) to move data to/from host memory, regardless of the bus type. (I am speaking strictly about data storage adapters/controllers). Bus mastering does not come cheap as it requires a significant amount of hardware/firmware to make it all happen. Futuer Domain boards, from my last contact, do not do bus mastering and are PIO boards, which is much simpler to do than first party DMA. This doesn't start to take into account the various features either adapter may or may not have above the data transfer method. --- Roy Neese Adaptec Senior UNIX/SCSI Software Engineer UUCP: convex!egsner!adaptex!neese Inet: neese%adaptex@cirr.com