More Haste Less Speed

By EDEN of Bounty

    Over the last month or two I have found myself and all those
around me becoming even more computer obsessed than usual. The main
source of this obcession appears to be the growing desire for ever
quicker and more powerful systems. (Oh 'er missus no!!)
    Back in the days when the Amiga was first launched the rates of
technical advance were fairly slow and the decisions about hardware
fairly easy. If you or your father owned a multi-national company
then you bought an A2000 if you were just an ordinary mortal you
bought an A500 and any other Amiga models were for people who read
DIY Electronics magasines or could repeat the first 20 op codes of
68000 machine code from memory. (Whatever that means)
    Over the last twelve months we have seen a vast increase in the
potential and actual computer configurations available. Now there is
more to deciding which computer hardware to buy than just working out
how much money you have and getting the most expensive model that falls
within your price range. The current options of hardware upgrades and
new machines are enough to keep even the DIY Electronics readers up
late at night working out all the combinations.
    What everyone is after is ever faster computers. What I have found
over the last two or three months is that most people are rather
confused about how to judge a computers speed and power from its
specification. In this article I shall try and explain what facors
affect the speed of you system and were possible give some advice
about how to get the best out of either your existing hardware or how
to upgrade it in the most sensible way.

CPU

    The CPU (Central Processor Unit) is the heart of your computer. It
is the brains and the work horse and is the fundamental key to the
performance of your computer system.
    On the Amiga series of computers the CPU is made by Motorola and
is from the 680x0 series (where x can be either 0,1,2,3 or 4).
    When considering the effect the specification of the CPU and the
effect it is going to have in the overall performance me need to look
for two different things.
    The first is what type processor is fitted to the machine or the
accelerator board. In basic terms, the higher the number the better
the processor is. The exact details of why each one is better than the
preceding version is the sort of thing that the majority of us
wouldn't understand even if we had access to the information. (Which I
don't). What I do know is that there is an important difference between
the 68000 and 68010 processors and all the later ones. This is that
the latter processors are able to deal with data in 32bit chunks
whereas the earlier 00 and 10's could only handle 16bits at a time.
This theoretically means that fitting one of the 32bit processors to a
machine with a 16bit CPU would double the speed. Unfortunately not
only is this sort of swap not possible without an accelerator
board but also the gains are not quite as great either because of
problems with memory speed (see below) or because sometimes it
just isn't necessary to manipulate such big numbers.
    The 500, 500+, 600 and most 1000, 1500 and 2000 models came as
standard with a 68000 processor, the 1200 has a 68020, the 3000 a
68030 and the 4000 a 68040 which is currently the most powerful chip
in the Motorola range (whispers of a 68050 not withstanding).

Clock Speed

    The next important topic when considering the effect of the CPU on the
speed of a computer is its CLOCK SPEED. Basically clock speed is the
tempo at which the CPU carries out the various mathematical and similar
operations that are its job in life.
    In principle then a CPU that runs at twice the clock speed of
another should result in a computer that is twice as quick. However
this is not the whole story as the computer is not only doing isolated
calculations but is also using memory and in the case of the Amiga
range of computers controlling dedicated chips for sound and graphics.
    Now we can begin to see the way in which different computers and
accelorators generate their speed. For instance lets look in principle
at the A1200.
    The A1200 has a 68020 CPU so we know that is potentially up to
twice as fast as an A500 just because its CPU can handle 32bit numbers
instead of 16bit ones. Next we look at the clock speed. Here the A1200
has a clock speed of 14MHz compared with 7MHz for the old A500. Again
in basic terms we can approximate this to a doubling of the speed of
the computer. We then MULTIPLY these speed increases together and we
get a potential increase of four times the speed of the A500. Once we
make allowances for the looses I've outlined above you might expect an
A1200 to be around three times as fast as an A500 for most tasks and
amazinglly enough thats about what it is!
    Now you can get accelerators for the A500 that consist of a
replacement 68000 chip running at twice the normal clock speed (14MHz
i.l.o 7MHz) but as this only gives around a 70% speed increase I
personally think you'd be better of saving your money until you could
afford a proper 32bit accelerator card.

Memory

    Memory also has an important effect on the speed of your computer.
I've already explained about how the '020 and higher processors are
able to deal with 32bit numbers but on the original Amigas the memory
was 16bit. This means that in principle just fitting a '020 processor
of the same clock speed to an A500 wouldn't result in any real
increase in speed because the memory would act as a bottle neck
slowing the processor.
    This is why most accelorators and  A1200, A3000 and A4000
computers are fitted with 32bit memory. It is also an important
consideration when A1200 owners start looking to upgrade their
machines. If they use PCMCIA memory cards which are only available in
16bit format, they risk slowing their machine down. Though of course
this doesn't apply to A600s.
    The second way that memory affects the speed of Amigas is due to
the  way that Amigas have custom chips controlling things like sound
and graphics. These chips need access to the computers memory to do
their jobs and the memory they use is called CHIP memory for obvious
reasons. The fact that at time they may need to get to this memory
before the CPU means that the CPU may have to 'wait its turn' for
access to chip memory with a resulting loss of speed.
    The rest of the computers memory that isn't affected by the custom
chips run on average just a bit quicker (normally around 15%) so it's
called FAST memory! Most Amigas leave Commodore with only Chip memory
so a little increase in speed is possible by fitting extra (FAST)
memory so long as the programmes you run are put into it which
generally happens automatically. (This is what the command
FastMemFirst is for.)
    The final way that memory can increase computer speed is unique to
some accelerators. This is that they use some of their inbuilt 32bit
memory to hold a copy of the ROM from the machine so that access to it
by a new 32bit processor is speeded up.

Co-Processors

    The last subject I want to cover is the one of maths
Co-processors. These are devices that the CPU uses as a sort of
Sub-Contractor for difficult (Floating Point) mathematical
calculations.
    Inorder for the CPU to correctly make use of the Co-Processor, the
programme has to have been correctly written to get any advantage from
it. As only a minority of people have machines with a maths
co-processor, software houses generally supply two versions of
software that could be enhanced by a MC-P (the sort of highly
mathematical programmes this applies to are Ray-Tracing Programmes).
    What this means in general terms is that unless you use programmes
that have a version that makes use of a maths co-processor you will
get NO ADVANTAGE from having one.
    If you want one though there are three to chose from. The first
two are the 68881 and 68882 the latter being a newer improved version
of the former. As with the CPU these have clock speeds which affect
their speed of operation. The other way to get a maths co-processor is
to get an A4000 or 68040 accelorator card as the 68040 CPU has a 68882
unit fitted internally to it.

What to Get

    Now I guess you would all like me to tell you exactly what
upgrades you should all be getting.

    Well I'm not so there!

    I honestly believe that it's a matter of individual choice and
circumstances. If you only play games then you really have no reason
to make any change whatsoever. If you must have more speed then the
latest A1200 and A4000 (bank robbery willing) are worth serious
consideration because you also get all the new graphics modes. If
however you've got a lot of hardware already then an 0x0 accelerator
makes some sense but people with a lot of hardware ought to be beyond
taking advice from me. (Infact they ought to be writting articles for
Bounty!!). Anyway I hope this has helped you in some small way to get
your machine to be as fast as Ben Johnson on Speed (though hopefull
not as stupid).


    Anyway thats enough of my waffle

    Cheers for now
		    EDEN.


P.S. If you want to see just how fast or slow your machine is compared
to the latest and greatest then  checkout SYSINFO in the PD section.