From: bloc1469@ee.ee.uwm.edu (Gregory R Block)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Future Amiga chipsets
Date: 23 Dec 1992 23:49:18 GMT
Organization: Electrical Engineering Dept. University of Wisconsin - Milwaukee
NNTP-Posting-Host: 129.89.2.33

In article <1992Dec22.200816.25990@sol.ctr.columbia.edu> jerry@msi.com (Jerry Shekhel) writes:
>David Navas (dnavas@oracle.uucp) wrote:
>: Well, personally, I would define crippled as any machine whose principle
>: communication's bus cannot transfer memory at anything even approaching a
>: rough approximation of processor speed.

>Does anyone else define it that way?  Face it, your definition is totally
>arbitrary.

No, it's not, it actually has a large basis in reality.  Let's take
the explanation a little further.  A bus, in theory, should be fast
enough to allow the CPU to transfer at speeds approaching or equal to
the rough approximation of the maximum speed at which the CPU can
transfer data.  Anything less, and the bus becomes a bottleneck which
must be dealt with.  When that bottleneck becomes large, such as a
33mhz i486 sitting on an ISA architecture, that becomes a crippling
bottleneck.  For ISA transfers, or anything of a similar reign whose
bus speeds are minute in size compared to the throughput that is
needed, the bottleneck cripples the system.

It's why so much research has gone into advanced bus technology, it's
why you're seeing some of the brand new innovations like SCI and other
scaleable buses come into existence, testing theories of operation.

>Really?  Well, in *my* universe the average hard drive isn't capable of
>more than, say, 1.5-2MB/sec, which ISA can easily deal with, with plenty of
>room to spare.  What about your universe?

So I suppose that just because your hard drive can go that fast, you
should be happy?  Look at the TIME for that transfer.  If you've got
an i486, you'd see much better use out of it--you're transferring
PACKETS of data, not byte by byte.  Those packets transfer faster, and
you can get back to REAL work with the CPU.  In the end, you're
spending less time waiting for your bus.

>I define "everyday tasks" for an expansion bus as "interfacing with normal
>peripherals found in most personal computers".  Is that an unfair definition?
>What good is a 550 GB/s bus if all your peripherals being cranked at once
>don't add up to 5MB/s?

Because unless you're doing polled io waiting for the bus to give you
each byte, you can spend less time transferring data and more time
doing things.  Don't make the mistake of believing that there's no
point to a faster bus when your throughput isn't there.  After all,
wouldn't it be nice to actually add memory?  Wouldn't it be great if
you could access your VRAM-based graphics card at something faster
than 8mhz?  Those kinds of things are REAL things.  They're not things
made up, people use buses for these kinds of things NOW.

>Where are you getting your information?  LocalBus supports any type of
>peripheral, not just video.  Look at a Gateway ad; most of their PC's now
>ship with LocalBus disk controllers.  Besides, the fact that a bunch of
>frustrated Amiga fanatics consider PC's "banally mediocre" has no bearing
>on reality.  Your attempt to pass it off as common knowledge is typical as
>well as laughable.

There are also serious problems with tying a bus too closely to any
particular processor.  Especially now that the 586 is on the way.
It's riscy, to coin a term.  :)

Frankly, I'd have liked to see a better bus standard come out of the
PC industry.

>Nice speech, but totally pointless.  Technology doesn't exist for technology's
>sake -- it has to be useful for human beings, *today*.  I have to have a 

Don't kid yourself by believing that people don't BUY technology for
technology's sake, though.

>computer *today*, and *today* there aren't any peripherals which would
>seriously tax the ISA bus.  Why should I spend extra for a fast bus and
>get *nothing*, when I could spend the money on a 24-bit graphics card and
>get *something*?

We're not talking about taxing an already flimsy bus, pal.  We're
talking about the ISA bus being a BOTTLENECK.  Something that would
tax an ISA bus?  The 24-bit graphics card you just mentioned.  If
implemented with VRAM, you'll spend your time waiting for your bus to
do your transfers.  Your solution?  Stick it onto the VESA bus.
LocalBus.  And screw forward-compatibility.  Because VESA is far, far
too tied to the current intel style of 486...  I can't venture to say
how or what kinds of modifications, visible or not, will be needed to
make it work with the Pentium.

The nice thing about Zorro III is that it really ISN'T tied.  It's a
really, really good bus design.  Something that is uncommon in the
world of intel-based PC's, unfortunately.

>Thanks for the advice :-P  Come on, face it.  Computers are tools.  When I'm
>in the market for a drill or a screwdriver, I'll take the one which is the
>most capable of helping me with the tasks I need to accomplish, even if
>there's another one whose specs look more macho on paper.

Consider this:  Your power screwdriver, your PC, has an engine which can
deliver the torque you want, but not at a good, fast speed.  Sure, it
gets the short screws in just fine.  But give a faster power screwdriver
to someone else, with an engine capable of delivering a faster speed,
and you'll see that person put that much more screws into the wall.
Given a limited number of screws, let's say, oh, 2/minute, you'll be
spending more time than he will using your power screwdrier on those
screws.  He'll have larger "gaps".  And on computers, it's those
"gaps" that let you get REAL work done.

>I ask you again.  What can't my ISA PC do directly because of ISA bus
>limitations?  Look, I'll even help you by mentioning one thing: DMA to
>memory above 16MB can't happen due to the ISA's 24 address lines, but then
>again, it's invisible at the end-user level.  Is there anything else?

Bottlenecks seem to be invisible to the user, too.  You don't notice
them unless you're on a system which makes it obvious...

Greg

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