Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!usenet.ins.cwru.edu!ncoast!davewt
From: davewt@NCoast.ORG (David Wright)
Newsgroups: comp.sys.amiga
Subject: Re: Re: A3000UX Seems Fated (Kill file alert!)
Message-ID: <1990Dec25.045537.13517@NCoast.ORG>
Date: 25 Dec 90 04:55:37 GMT
References: <39228@nigel.ee.udel.edu> <1990Dec17.052316.19609@NCoast.ORG> <1990Dec24.220257.12208@ddsw1.MCS.COM>
Organization: North Coast Computer Resources (ncoast)
Lines: 63

In article <1990Dec24.220257.12208@ddsw1.MCS.COM> karl@ddsw1.MCS.COM (Karl Denninger) writes:
>"Seldom" does not equal "not available" on the RAM expansion.  Check with
>the 486 owners -- most of them can do 64MB on the motherboard, using 4MB
>SIMMS.  No problem; plug and play.
	Sure, but most people consider the '386 similar in performance to an
'030 (though I am not one of them. In real-world use I have found the '030 to
be faster). If you look at systems designed around the '040 you might also find
that. I am also sure it has something to do with the price and market. No one
would buy a '486 system that handled that much memory just to run DOS
software, it would most certainly be for Unix. I am also sure that if you are
using 4mb SIMMs (which aint cheap by far), you will be quite limited in your
memory configuration, as you useually are when you use a system (like the
Amiga 3000) that can handle 256k and 1mb chips. You either have a little
RAM, or a lot of RAM, without small increments inbetween. For 4mb chips I
would assume this would be even worse.
>This is a non-issue.  The ISA PC bus can pass 8MB of data per second.  The
>best SCSI fixed disks we have available today can do 2MB/second.  MOST disks
>cannot sustain that kind of transfer rate for long, even in synchronous
>mode.
	Hogwash. It may be able to do BURSTS of that high, but I would like to
see an 8 Mhz bus do 8mb a sec for any amount of time, even if the controller
was taking over the machine to do it.
>
>SCSI has a maximum transfer rate of 5MB/sec.  That is STILL well under the
>ISA bus machine's bus bandwidth.
	You mean SCSI-I here, not SCSI-II.
>
>Since there is little or no reason to put anything ELSE on that bus other
>than perhaps video, you have 4X the needed processor <> disk bandwidth.
>Anyone who tries to sell you more bandwidth than you need is a thief -- of
>your money, that is.
	Oh? Like maybe 64 port I/O boards? Or maybe even 16 port boards? Just
how many users are you trying to stick in there without using some kind of
I/O board in the ISA backplane? And all these other boards you are adding
are further cutting down on the available bandwidth of the ISA bus. Next,
if you are trying to run X on a VGA board, that will suck up a lot of the
ISA bus bandwidth right there, not to mention the main CPU time. And finally,
have you ever used a SCSI system with more than one drive? Don't forget that
ALL the drives on a single host adapter share the same data port, and therefore
help to eat up any remaining room that might have been left. If you have 2 or
three SCSI devices, (best example would be a hard disk and a tape drive,
with the tape drive backing up the hard disk), it is EASY to hit the limit
of the ISA bus, even if the drives only do 2mb/sec. And as many of the better
drives have on-board caches, which do read-ahead, you are likely to get big
gushes of data coming in, from each device on the SCSI bus.
>
>Note that "real" controllers for the ISA bus, those which do bus mastering
>(AHA1542B for example) are here and do work.  They take nearly all the load
>off the processor, do intelligent seek ordering, overlapped command/data
>requests, and all kinds of other wonderful things.
	Agreed. And using a caching controller can help a lot too.
>Today EISA is a waste of money, as is MCA.  ISA is more bus than you can use
>for disk I/O.  Hell, I can do better with an ISA PC than most workstations
>in disk performance with a little judicious tuning of disk parameters!
	Depends on who you are selling to. To Joe Blow off the street, that's
true. But this thread was about the performance of ISA systems as Unix
servers/workstations. Jow Blow doesn't do this kind of work, and certainly
wouldn't pay the >$6000 for an entry level 16 user system. The only way ISA is
"more than you can use" is if you have ONE device attached to it, and don't
expect to do lots of large-scale data transfer (like swaps).


			Dave