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From: mju@mudos.ann-arbor.mi.us (Marc Unangst)
Newsgroups: comp.unix.bsd
Subject: Re: [386BSD] Creative Labs CD-ROM drivers - Any progress?
Date: 26 Jan 1993 17:38:59 -0500
Organization: The Programmers' Pit Stop, Ann Arbor MI
Lines: 31
Message-ID: <1k4ei3INN6kl@mudos.ann-arbor.mi.us>
References: <1993Jan20.050758.26030@udel.edu> <1993Jan26.073432.16561@ntuix.ntu.ac.sg>
NNTP-Posting-Host: mudos.ann-arbor.mi.us
In article <1993Jan26.073432.16561@ntuix.ntu.ac.sg> eoahmad@ntuix.ntu.ac.sg (Othman Ahmad) writes:
>Why do say we are stupid when the ATBus version is surely faster than the
>SCSI version?
I'd be interested in hearing why you think this is so. It would seem
to me that the SCSI CD-ROM drive would be faster than a SonyBUS drive,
if indeed there is a performance difference (which I doubt, see
below). Why? Well, the controller/host adapter provided with the
cheap SonyBUS drives is usually an 8-bit unit that is engineered with
price in mind, not performance -- since the SonyBUS units are usually
the cheaper, lower-end devices. With a SCSI device, the manufacturer
doesn't have to include a host adapter in the total development and
manufacturing budget, and so can dedicate a higher percentage of the
total budget to the drive itself. In addition, SCSI host adapters (at
least the ones I'd use in *my* system) are usually 16-bit or 32-bit
cards that do bus-mastering DMA.
However, I doubt there's going to be any noticable performance
difference at all. Keep in mind that with a CD-ROM drive, the
bottleneck is getting the data off the CD, not getting the data from
the CD-ROM drive to the host. The CD<->drive transfer rate is going
to be 150K/s (or 300K/s, if you have one of the fancy double-speed
drives), no matter what you do with the host adapter; 150K/s is much
lower than the maximum transfer rate of even an 8-bit card using
programmed I/O.
--
Marc Unangst, N8VRH | "Of course, in order to understand this you
mju@mudos.ann-arbor.mi.us | have to remember that the nucleus of the atom
| is squishy."
| -W. Scheider, from a Physics lecture