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Path: sserve!newshost.anu.edu.au!munnari.oz.au!bunyip.cc.uq.oz.au!harbinger.cc.monash.edu.au!msuinfo!uwm.edu!cs.utexas.edu!uunet!ftpbox!mothost!delphinium.cig.mot.com!declrckd From: declrckd@rtsg.mot.com (Dan J. Declerck) Newsgroups: comp.os.386bsd.questions Subject: Re: CDROM support Date: 10 Jan 1994 16:51:05 GMT Organization: Motorola Inc., Cellular Infrastructure Group Lines: 37 Message-ID: <2gs11p$58g@delphinium.cig.mot.com> References: <2g5qaq$ng0@u.cc.utah.edu> <DykkFc3w165w@oasys.pc.my> <BLYMN.94Jan9192240@siren.awadi.com.au> NNTP-Posting-Host: corolla17.rtsg.mot.com In article <BLYMN.94Jan9192240@siren.awadi.com.au>, Brett Lymn (master of the siren) <blymn@awadi.com.au> wrote: >>>>>> "Othman" == Othman Ahmad <othman@oasys.pc.my> writes: >In article <DykkFc3w165w@oasys.pc.my> othman@oasys.pc.my (Othman Ahmad) writes: > > >Othman> terry@cs.weber.edu (A Wizard of Earth C) writes: > >>> the SoundBlaster SCSI, which wants a CPU-intensive driver to push >>> its bits for it, unlike decent, God-fearing SCSI cards that will do >>> bus-mastering >Othman> Beware though that direct memory read can be faster than any >Othman> DMA given the right processor. > >Uh... ok tell us about it, this should be a doozy. Personally I >cannot see how any processor doing instruction fetch, decode, address >calc, read, instruction fetch, decode, address calc, write ... and so >on could be faster than DMA stuffing data into memory and remember we >are talking disk transactions here not single byte transfers. > The REP operation on Intel parts is similar to the DBcc operation on Motorola parts, in the effect that once this 2 instruction loop is fetched, no further opcode fetching takes place until it is complete. Also, you must remember that some systems have cache, which allow the processor many bus cycles for every DRAM memory cycle. This is true on every 486DX system. The BIOS for the original IBM AT uses NO DMA to interface to the drive controller. the 286 was faster thyan DMA for DOS (Unix is a different story). -Dan -- => Dan DeClerck | EMAIL: declrckd@rtsg.mot.com <= => Motorola Cellular APD | <= =>"Friends don't let friends wear neon"| Phone: (708) 632-4596 <= ----------------------------------------------------------------------------