gauging interest in VAX 6000-530

From: Mike Cheponis <mac_at_Wireless.Com>
Date: Tue Oct 26 00:08:21 1999

Peter, I do hope your arm heals quickly.

On Mon, 25 Oct 1999, Peter Pachla wrote:

> >....I think single-user; I run single-user machines....
>
>Exactly, Mike you're looking at just ONE sector of the computer world. What is
>important to you is of no consequence to a vast number of other
>people/corporations who need to support multiple users and process vast
>amounts of data.

Which is going to be done on servers.

> >....The future is single-user with vast network-accessed databases.
>
>RUBBISH, you're making assumptions based on your own view of the industry. In
>the real world there is a need for both single user systems/workstations AND
>(comparatively) large multi user installations.

I don't believe it. Can you please give me some specific application that
is better served by some timesharing system?

>But then, of course, I think you probably realise this and are just offering
>us more flame bait?

I have never offered flame bait on this discussion. I have tried to
understand other points of view, and to be corrected when I was wrong. I'm
a little too old to be throwing out flame bait.


> >BUT, I would like the Vax Lover Crowd to acknowledge that they integer
> >performance of their machine is pathetic.
>
>More flame bait. Do you REALLY think that making assertions such as this is
>going to make anyone on the other side of the fence anything but
>defensive?????

Peter, I have -tried my damndest- to -prove- beyond the shadow of a doubt
with facts and data to support that assertion. Look, I'm getting
tired of repeating this.

What I'm TRYING to do is to understand the performance of old machines
in terms of new machines; what I don't understand is why so many people
are uptight about this. Heck, we might all even learn something, eh?


>As others have already pointed out, integer performance/MIPS/drystones etc is
>NOT a good indicator of overall SYSTEM performance. THAT is what is of
>importance at the end of the day.

BUT, BUT BUT! It -is- true that a .... is 2 to 3 times ... Right? Admit
it! That's a very very simple statement of fact, why is this -sooooooo-
difficult for so many on this list?



>A personal example....in the mid '80s I was working in the video games
>industry writing software for Atari and Commodore systems (Atari 8-bit,
>C64/+4, Atari 7800). I used to assemble my programs on the Atari and transfer
>them to the target system rather than use a cross assembler on a PC. Why?
>Because although the PC I had access to ran a V20 at 8MHz compared to the
>rather pedestrian 1.79MHz of my Atari's 6502 the PC took roughly 4 times
>longer to do the same job - even with the obvious advantage of having a hard
>drive. If you want the damn figures I expect I still have them somewhere
>(though it would mean digging out my Atari system to access the data).

I would always choose the faster system, all other things being equal, too.

>It was a simple case of superior SYSTEM architecture.

And, no doubt, crummy PC s/w.


>Two 1MHz busses will be faster than a single 2MHz bus if they are being used
>for different purposes, such as one for I/O and one for memory accesses.

But my point is that one 4 MHz synchronous bus is going to be faster than
two 1 MHz busses in all cases.

Nonetheless, what you say is not necessarily true.

For example, assume that your hypothetical case of two 1 MHz busses, and
assume that the I/O bus and the Memory Bus are saturated.

If these I/O and memory accesses were multiplexed onto a 2 MHz bus, then,
they'd be one I/O then one memory then back to I/O etc, perfectly interleaved.
Anything less that this, and the busses would not be saturated.

In that case, the 2 MHz bus would equal the 1 MHz bus.


Now, what about the case for random arrivals? I'm not going to fully
derive this, but consider an I/O request frequency of Fio
and let Fm be the frequency of memory references.

If you have a system that is mostly doing computation, then Fio << Fm
and therefore, on a 2 MHz bus, the memory bandwidth is > 1 MHz (which is
the MAX you can get on the other bus).

Similarly, if you're doing mostly I/O, then Fio >> Fm, and you can do
up to two times the I/O on a single 2 MHz bus than you can do on a single
1 MHz bus.


I think I have just proven that multiple busses are an architectural disaster.
Failing at that, I have proved your original assertion as being incorrect.

Multiple busses -are- useful to match the slow speed of I/O to the fast
speed of the processor's memory system. And, clearly DEC believed in the
more busses the merrier: UNIBUS (tm), MASSBUS, CI Bus, SBI Bus, etc.

But if the I/O can keep up, then separate busses are a disaster.


>Particularly in the case of the PC the single expansion bus is a major
>bottleneck. The original design had all I/O, memory, memory refresh etc ALL
>done over a single bus.

You'll note that I was not trying to defend the original PC.

>Although things have gotten a lot better with the introduction of MCA, EISA,
>VL and PCI, separate RAM busses etc there's still a long way to go. We still
>effectively have a single bus down which we're trying to shovel the majority
>of our data.



> >After all, at -some- point, all these busses have to get their data
> >into/out of the CPU....
>
>No, at some point all these busses have to get their data in/out of MEMORY.
>Polled/interrupt driven I/O is at best extremely wasteful of processor
>time....this is why I personally use SCSI in my PC in preference to IDE (which
>makes it ALMOST usable).

Peter, you'll note that I said that there are some cases where "channel-to-
channel" I/O occurs, but I call that "Simulfax Shuffle Time" (after
Firesign Theatre) - that is, in general, except for the special case of
file copy for backup, moving data around without processing it is a logical
and architecture error (or at least, inefficiency).

And, data into or out of memory -eventually- must go into and out of the CPU,
in general - else, there's no processing actually occurring. And I'm
afraid I don't agree with the one poster that was making the case that
moving data around should be considered processing, for reasons, above.


> >....and it does show that there are other busses available on a
> >PC, yes? (Which was my original point.)
>
>But with just ONE bus in the system you STILL have a bottleneck.
>
>It doesn't matter how many lanes you have on a single motorway, or how fast
>your car is, when you have a lot of traffic on the road you still get traffic
>jams and major bottlenecks at junctions and on/off ramps....


This analogy is flawed, I'm afraid.

A better example is: how much lead can you deliver to a load with two guns
rated 1 Mega-Bullets per Second vs one gun rated at 2 MB/Sec?
Answer, of course: They produce the same amount of deposited lead on the
target.

Another analogy might be:

I have a Racecar, a family car, a truck, and a bicycle. (Roughly SBI,
CI Bus, MASSBUS, and UNIBUS).

But if I had all Racecars......


> TTFN - Pete.
>--
>Hardware & Software Engineer. Sound Engineer.
>Collector of Arcade Machines, Games Consoles & Obsolete Computers (esp DEC)

-mac
Received on Tue Oct 26 1999 - 00:08:21 BST