From: phd85@seq1.keele.ac.uk (D.H. Holden)
Newsgroups: comp.arch
Subject: Re: CPU and speed question
Keywords: thanks
Date: 8 Sep 92 11:31:13 GMT
Organization: University of Keele, England


In article <4028@keele.keele.ac.uk> 

 
  i wrote an article asking
  about worksations and PC and CPU speed, I'd like to thanks every
  one who replied ( much too many to list!!)
  I have a slight dilemma as to how to summarise the answers, 
  All were thoroughly informative and helpful, and i'll be checking
  out some of the recommended books, the problem being that quite a
  few were from people working with companies who produces or use the
  chips mentioned , each giving their own somewhat wry :) comments on competitor
  offerings, quite amusing. As im not a computer professional i'm not
  really qualified to pick out individual pieces of advice and 
  summarise therfore 
  i'm posting the following reply as the one that gave the most
  numbers!!

P.s.  to Robert Block, sorry Robert but my mailing program didn't
recognise the address you gave so I could not reply. Sorry.
   
In comp.arch you write:
> Hi,
>    I was wondering if any one could resolve my confusion,
>    what is it that makes a workstation faster than a PC
>    apart from the operating system.

  The Operating System actually doesn't make the machine faster (well,
I suppose it could, but it doesn't necessarily), but offers more features
to the user, so they don't have to acquire application programs to do what
(IMHO) the OS should be doing.

  In a nutshell, it's faster because the people who buy them want more
speed, so they'll pay more.  Exactly like supercomputers.  Take, for
example, the system bus.  PC's have a bus going about 10 Megabits per
second, with IBM's MicroChannel Turbo whizzing along at 30.  The Sun
Sparcstation 1 uses SBus for cumminication between peripherals, which
starts at 80 MBits/second.  The old Sparc 3's used a VME bus, running at
28 Mb/second.  That's for peripherals.  What PC's are discovering -- a
local bus, is nice to have to communicate between CPU, memory, and video.
On the workstation side, it's used for communication between multiple
CPUs.  Sun's MBus operates at about 300 MBits/second, SGI's at over 500.
Sun has something called XBus, designed by Xerox, which is supposed to be
used for a single bus handling ~64 CPUs.  I assume it's extremely fast.

  Of course, all this costs money, which is why it shows up in $10,000+
workstations first.  But then look at some of the supercomputer stuff,
where HIPPI channels to the disks run at 800 MBits/second, and God knows
what their internal busses run at.  Very bloody fast, and very bloody
expensive I'm sure.


>    Because I've just read a article about a PC with a
>    50Mhz clock, would this be faster than say a sun 
>    workstation with 25mhz clock?

  Again, to sum up the argument, clock speed only matters between the
same design.  Actually, it does have _some_ bearing, but you can't say
that a 25MHz 486 is necessarily faster than a 25MHz 68040.  They're
completely different designs.  And a SPARC chip is even more different.
At the same clock speed, your SPARC will run circles around the 486
_for_certain_operations_.  For other operations (string stuff would be
likely) the 486 would win.  The point of the SPARC design (as in all
RISC design) is to optimize those operations you consider most likely.

  Let's take a look at the SPEC92 numbers for a 50 MHz 486, a 25 MHz
SPARC, a 40 MHz SPARC, and a 40 MHz SuperSparc (TI Viking).  Be aware
that the SPARC systems are more expensive, but they also have quite a
few bells and whistles that you don't get (or can't get) on the Intel
box.

Designer Chip     Speed   Spec92Int  Spec92FP  MFlops
-------- -------- ------- ---------- --------- ---------
Intel    486      50      30.1       14.0       3.0 (A 486/33 got 1.4)
Cypress  SPARC    25      13.8       11.1       1.8
Cypress  SPARC    40      21.8       22.8       4.0
TI       SPARCv8  40      52.6       64.7      17.2

Hmm.  The Cypress SPARC (v7) and the SuperSparc are running at the
same clock rate (40 MHz), but the SuperSparc is quite a bit faster.
The SuperSparc happens to be a superscalar design, capable of executing
3 instructions every clock cycle.  Advances in technology..  The 40
MHz Cypress Sparc beats the 486 running at 50 MHz in floating point.
FP is important to a lot of workstation buyers (such as ourselves), and
even twice the 486 isn't enough for our purposes.  BTW, just so you
don't believe PC Week, or Everex ads, the Cray X/MP runs at 184 MFlops,
and the Y/MP C90/16 at 9715.  Even the old Cray XMS (running at 18 MHz)
gets 34 MFlops.
[These numbers are from Dongarra's Summary of Linpack numbers from netlib]

  BTW, Intel says the P5 will be twice as fast as the 486.  Draw your
own conclusions as to it's impact on workstation buyers from the above
numbers.

>    I also read that dec are bringing out a new chip
>    that can manage 200Mhz, is'nt this a massive jump
>    from current chips, I thought the fastest intel chip
>    only did 66Mhz.

  One could make the analagy of Clock speed in computers to HorsePower
in cars.  The more HP, the faster, in general, and within a design, it
is almost always true, but there are an awful lot of other things to
consider.  The Yugo with 1000 Horsepower is going to spin those little
tires around and make an impressive amount of noise, but the 200 HP
NSX is going to win the race.  Of course, DEC doesn't make Yugos...
(they make diesel Mercedes! :-)

  200 MHz is impressive.  They can take 4 cycles to do an operation that
would take a 50MHz machine 1 cycle, and achieve a result in the same
time.  There are some problems with running at that speed however.  Power
dissipation is one -- there's a reason supercomputers have air-
conditioners!  (The Cray Y/MP runs at 240 MHz, the NEC SX-3 at 344)  I
heard from someone who saw a pre-release Alpha workstation that it had
warped the case above the chip (I think it puts out in excess of 20 watts
which is plenty hot!).  DEC says they'll solve this problem, of which I
have no doubt, but there are others.  It'll be a nice addition to the
field however.  Hopefully it'll get the other manufacturers moving!

  Looking at the latencies and throughputs for some basic operations,
one can see some interesting things going on.  The 88110 and SuperSPARC
are running at 40 MHz, and should be at 50 or above by the time Alpha
sees market.  This leaves Alpha running at 3-4 times faster than the
others, depending on which version.
  The first number is when the chip will accept more input (they're all
capable of handling multiple instructions at a time), and the second
number is when the answer comes back.  The 88110 and Alpha are 2-scalar,
so they can do 2 at a time, the SuperSparc 3-scalar, so it can run
three operations at a time.  Each has different combinations it allows.

Operation      Moto 88110    TI SuperSPARC     DEC  Alpha

Int add/sub        1/    1        1/   1          1/1-2
Int mul            1/    3        4/   4      19-23/19-23
Int div           18/   18       18/  18          ---
FP add/sub         1/    3        1/   1          1/ 6
FP mul             1/    3        1/   3          1/ 6
FP div         13-26/23-26    6- 9/ 6- 9      30-63/30-63
FP sqrt            ???        7-12/ 8-12          ???

 The Alpha doesn't have floating point divide, so it has to emulate it
with multiply.  This is what the old v7 SPARCs used to do.  Wasn't it DEC
who was one of the loudest to point this out as a deficiency? :-)
  So, on Int add and substract, the Alpha will blow by the others.  On
Int multiply and divide, and on FP divide, the other two will be _faster_,
even with the Alpha chip running at 4 times the clock rate!  For FP
multiply, Alpha should be about twice as fast, and who knows about
square root -- Sun/TI were the only ones to post this info.

>    Hope this is the right group to post this, comp.arch
>    sounded right,

  This, or comp.benchmarks, is certainly the right group.

>    cheers, 
>		Dave

  Hope you survived my talking your ear off...  You can post this in a
summary if you want (I really hope the information is accurate!  I'd
like to know if it isn't).
--
Dana Jacobsen
jacobsd@solar.cor2.epa.gov
jacobsd@cs.orst.edu