Path: utzoo!attcan!uunet!lll-winken!ames!elroy!ucla-cs!oberon!randvax!ism780c!ico!clover!rcd
From: rcd@ico.ISC.COM (Dick Dunn)
Newsgroups: comp.unix.xenix,comp.unix.i386
Subject: Re: ESDI vs SCSI (bus speed)
Summary: bus speed bs DMA speed
Message-ID: <15739@clover.ICO.ISC.COM>
Date: 15 Apr 89 03:53:01 GMT
References: <98520@sun.Eng.Sun.COM> <5436@lynx.UUCP>
Distribution: na
Organization: Interactive Systems Corp, Boulder, CO
Lines: 20

In article <5436@lynx.UUCP>, m5@lynx.uucp (Mike McNally) writes:
> In article <98520@sun.Eng.Sun.COM> williamt@sun.UUCP (William A. Turnbow) writes:
> >	First off you have limiting factors in bus transfer speed.  On an
> >AT bus I believe this is something like around 4-5 Meg/sec.  
> 
> Try 0.5 Mbytes/sec, not 5.  The DMA controller on the AT takes a long
> time getting on and off the bus...

Keep trying.  Turnbow said the AT bus, not the DMA controller.  The bus is
a whole lot faster than 0.5 Mb/s.  Hard-disk transfers on AT-style machines
are traditionally done with programmed I/O, NOT with DMA (even in the
BIOS).  The disk controllers have sector buffers, since they have to do the
ECC before anything's ready anyway, so it's not like the PIO has to wait on
a disk.  The business of hand transfer off a disk is probably strange to a
lot of people coming from big-machine backgrounds--it certainly was to me,
escpecially when I found that the floppy *does* use DMA!  But it's not
really all that bad...I notice we're running ESDI 63-sector drives at 1:1.
-- 
Dick Dunn      UUCP: {ncar,nbires}!ico!rcd           (303)449-2870
   ...Never offend with style when you can offend with substance.