mac comps

Ian Molton spyro at f2s.com
Fri Oct 18 13:23:09 PDT 2002


On Fri, 18 Oct 2002 18:59:35 +0000 (UTC)
JDrabb at darden.com ("James Drabb") wrote:

> > Actually, the A7000+ is an OK performer - its no games machine, but
> > it'll do better desktop publishing than a PC with 10 times its spec.
> > 
> > -- 
> 
> Still, how fast can a 300 MHz RISC be?

Quite nippy actually. Bear in mind a lot of RISC OS is written in
assembler by people who KNOW how to write assembler.

> It can still only do at most 300 million ops per second.

Wrong. you can actually do up to about 2.5 times better than that as the
later ARMs are superscalar (I think thats the term used for a CPU
capable of executing >1 insn at once, I always mix it up with some other
term).

For example, on some ARMs, a 32 bit MUL takes 3 cycles and you can
execute any non-MULL non-conflicing instructions in the following 2
cycles (and its actually possible to do so on ARM as its register rich
(15 general purpose, and the program counter available to usermode
code)).

>  Versus a cheap celeron/duron
> running at 1.x GHz or a P4 at 2.x GHz.

True, a 1-2GHz cel/dur will blow it away in raw grunt, however, compared
to a 300MHz part, the StrongARM does very well indeed.

the SA pipeline is only 5 entries long, and branches take a MAXIMUM of 3
cycles (if in the insn. cache, of course). loads / stores from cache
take 1 tick. it has powerful multiregister load/store operations too.

>  Was that a typo or do
> they really have 64 MB of L2 cache or did you mean main memory?

Both, sorta. the 'kinetic' ones (with the 300MHz CPU) have 64MB of RAM
on the card, connected to the CPU at 66MHz. the main memory bus
(remember the original machine is over 8 years old) is only 16MHz. the
on-cpu-card RAM could be considered L2 cache, is a loose sense. hence I
wrote it in invert commas.

The thing is, though, that RISC OS programmers have simply tended to be
very good - for example, my **8** MHz ARM2 based system (ARM2 has *no*
cache) with shared video and system RAM, now 15 years old, is capable of
rendering its *ENTIRE* GUI in antialiased vector fonts, at any scale,
resolution, or orientation. AND it can do it at a useable speed. Its
video chip has NO acceleration functions, to boot.

compare to KDE / gnome2 on current hardware, just barely managing the
same task...

Did I mention, the old Acorn was doing *subpixel* antialiasing?

Impressive machines, despite lacking raw grunt. The only lacking thing
is an FPU, but ARM hackers have done very well without it - eg. an MP3
player running in <5% CPU time on a pure integer machine without
halfword stores (which strongarm supports, but the RISCPC cant). FPUs
give one benefit - superscalarity. its proven that they dont actually
improve performance over well written integer / fixed point code.

;)
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