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From: michaelv@iastate.edu (Michael L. VanLoon)
Newsgroups: comp.os.386bsd.misc
Subject: Re: SCASI or IDE disk?
Date: 11 Aug 94 03:46:27 GMT
Organization: Iowa State University, Ames, Iowa
Lines: 51
Message-ID: <michaelv.776576787@ponderous.cc.iastate.edu>
References: <salem.136.2E48D0EF@hauk.hsr.no>
NNTP-Posting-Host: ponderous.cc.iastate.edu
cc: salem@hauk.hsr.no (Salem, Lazaro)
In <salem.136.2E48D0EF@hauk.hsr.no> salem@hauk.hsr.no (Salem, Lazaro) writes:
>I have a bought a PC-clone,i486/DX33 Mhz, with 16Mb RAM (60 ns), 256Kb cache,
>ISA bus + 2 VL bus on board with 256 Kb cache, 2 FDD (3,5/1.4Mb & 5.25/1.2Mb),
>-> SCASI Adapter Card (ADAPTEC 1542CF),
It's *SCSI*! Repeat after me: S - C - S - I
It stands for Small Computer Systems Interface
>-> 2 IDE HD controllers
>a Quantum 420Mb.
I have one of these -- it's an excellent drive.
>I am not sure about the convenience or not of buying a SCASI or an IDE disk.
>I can get any of them at the same price (almost), and since I have both
>IDE and SCASI controllers I wonder what other considerations shoud I take to
>make my mind.
There is a big win in getting SCSI devices. SCSI is faster and
flexible than IDE, and a SCSI controller takes a lot of load off the
CPU, where IDE makes the CPU do all the work in transferring files.
>As far as I understood (was told) there would not be any sensible difference
>for a one or two HD stations ("the botleneck is the bus speed" they said).
This is untrue, to a point. Through an ISA bus, you may not get any
extra speed with SCSI on raw disk transfers. However, since the SCSI
controller is doing all the work as a bus-master, your CPU will be
free to do other things while the transfer is taking place. With IDE,
the CPU is totally dedicated to writing every byte out and reading
every byte in from the IDE drive in a tight loop, meaning it can do
nothing else while an IDE transfer is in progress.
So, even if disk transfers aren't any faster for you, your machine,
overall, will be less busy with SCSI, and may perform more "smoothly".
Now, in your case, you have a very slow SCSI card, so the bus speed is
going to limit you more than anything else. You might start out with
your current SCSI card, than upgrade to a BusLogic SCSI card that
works in one of your VLB slots (four to eight times faster) at some
point in the future, which will work with your current SCSI drives.
--
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Michael L. VanLoon Iowa State University Computation Center
michaelv@iastate.edu Project Vincent Systems Staff
Free your mind and your machine -- NetBSD free Un*x for PC/Mac/Amiga/etc.
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