Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!ralf
From: ralf@b.gp.cs.cmu.edu (Ralf Brown)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Transfer rates
Message-ID: <7358@pt.cs.cmu.edu>
Date: 20 Dec 89 03:42:29 GMT
References: <44807@bu-cs.BU.EDU> <1989Dec16.192948.27568@hellgate.utah.edu>
Organization: Carnegie-Mellon University, CS/RI
Lines: 24

In article <1989Dec16.192948.27568@hellgate.utah.edu> u-gclapp%ug.utah.edu@cs.utah.edu (Glenn Clapp) writes:
}In any case, transfer over the SCSI may be very high, but it still has
}to get the data into the PC via the out-dated AT bus at 8MHz (some 
}are faster, but this get's dicey (I know, just try an ATI VGA Wonder
}in a 12MHz bus and see what happens).  The AT bus has a maximum
}*Theoretical* transfer rate of 1Mb/s, but in practice the maximum is
}somewhat less.

Better not tell the HD controllers with hardware disk caches that blast 3-4M/s
over the AT bus....  The AT bus is nowhere near the bottleneck with current
hard disk technology.  MFM drives do up to 500K/s, RLL up to 750K/s, and
ESDI do up to 1M/s for 10MHz controllers (there are also some 15 and 20MHz
controllers available, but I wonder whether current hard disks could actually
make use of the extra speed--you'd need about 68 sectors per physical track
to max out a 20 MHz controller).  Compare that to a bus bandwidth of 5.33M/s
for an 8 MHz/1ws bus doing 16-bit transfers.  SCSI can theoretically do 4M/s,
but that assumes that both the hard disk and the host adapter can keep up
(I think the new SCSI II does 10M/s).

-- 
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