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Xref: sserve comp.os.386bsd.questions:5615 comp.periphs.scsi:14386 Path: sserve!newshost.anu.edu.au!munnari.oz.au!yoyo.aarnet.edu.au!myall.awadi.com.au!myall!blymn From: blymn@awadi.com.au (Brett Lymn) Newsgroups: comp.os.386bsd.questions,comp.periphs.scsi Subject: Re: CDs and SCSI Date: 3 Oct 93 17:15:51 Organization: AWA Defence Industries Lines: 22 Message-ID: <BLYMN.93Oct3171551@mallee.awadi.com.au> References: <CE29yI.IKt@festival.ed.ac.uk> <CE2AF7.AA@veda.is> <289fup$967@hrd769.brooks.af.mil> NNTP-Posting-Host: mallee.awadi.com.au In-reply-to: burgess@hrd769.brooks.af.mil's message of 28 Sep 1993 08:58:35 -0500 >>>>> On 28 Sep 1993 08:58:35 -0500, burgess@hrd769.brooks.af.mil (Dave Burgess) said: Dave> In article <CE2AF7.AA@veda.is> adam@veda.is (Adam David) writes: Dave> }richard@castle.ed.ac.uk (Richard Tobin) writes: Dave> } Dave> }You might find that they are not DMA busmasters, so you could end up using Dave> }more CPU cycles pushing all that data around. You might also find them slower Dave> }for this or any other number of reasons. Wasn't someone working on an ST-02 Dave> }driver? Dave> } Dave> Isn't the amount of CPU used for these types of transfers something like Dave> 17 cycles + 2/byte? At 20Mhz, that is a herd of data in a second. Yep but it is also a herd of CPU cycles that are not being used for reading keyboards/serial ports/updating screens - using the CPU to transfer data from interface to memory is not a good use of a CPU. Getting the device to dump data into memory is far better because it runs at the bus DMA speed (4 - 5 Mbyte/s) instead of 1Mbyte/s of the CPU shuffle. -- Brett Lymn