From: lupe@alanya.isar.muc.de (Lupe Christoph) Subject: Re: Coherent vs. Linux - a comparo Date: Mon, 5 Jul 1993 06:32:26 GMT
zblaxell@undergrad.math.uwaterloo.ca (Zygo Blaxell) writes:
>>> XWindows is a great thing but it requires a lot of system. The mips
>>>machine I had came originally with 32 meg of ram. It ran so-so until
>>>I upgraded to 64 megs.
>>
>>That's a MIPS machine - I run XFree86 1.2 on a 386/25 with only 8 megs
>>of memory, and it works great. Scrolling speed could be a notch
>>faster, but that's not a problem with memory, that could be fixed
>>with a faster processor or an accelarated video card.
>MIPS (and probably SPARC as well) are RISC architectures. They use
>32-bit instructions which don't do very much by themselves. The 386
>uses 8-bit instructions (at a minimum anyway) and is a CISC
>architecture. Some 386 instructions require 8 or 9 RISC instructions
>(32-36 bytes) to accomplish the same result. MIPS machines make the CPU
>as simple (and consequently fast) as possible, and compensate by
>throwing lots of memory (RISC code is easily 20 times as big as CISC
>code that does the same thing) and intelligent hardware at it. 386
>machines make the CPU as powerful as possible, but most of the 386's
>I've seen are still running XT- or AT-class peripherals.
Boy, do you have misconceptions! Please take the fugly architecture
of both the x86 and the PC into account. As a general rule, RISC code
*is* larger than CISC code. But you contradict yourself if you say that it
takes "8 or 9 RISC instructions ... to accomplish the same result" and then
go on to say "RISC code is easily 20 times as big as CISC code ...".
First of all a RISC machine has more registers, so it does not have
to use the stack as much as an x86 with it's few registers. Then, the
factor is much smaller, in the range of 1.2 to 1.7, I guess.
Just compare the number of transistors the Pentium needs with,
for example, the SuperSPARC. The same, you say (3.1 million)?
Then deduct the transistors used for the internal cache (Pentium:
16 kB, SuperSPARC: 36 kB; I don't know how many transistors per
bit for the Pentium, the SupeerSPARC uses 6).
It is also not true that RISC machines throw memory and "intelligent
hardware" at the problem. I have yet to see a caching disk controller for
a RISC Unix box. In general, memory requirements are the same.
Look at Solaris on SPARC and on x86.
>Please stop comparing MIPS machines to 386 boxes. It makes as
>much sense as comparing apples to pumpkins.
Stop comparing dissimilar OSes, like some MIPS Unix and Linux.
>>>As for processor power, you need a lot to make xwindows run. I'd think
>>>a 40mhz 386 would be barely adequate.
>>[disagreement]
>I second the disagreement. The whole point of X-windows is that the CPU
>doesn't have to have anything to do with graphics performance. Get a
>decent graphics card instead.
You sure? I thought the whole point of X is that the window code
is isolated from the application program, and that it is possible
to put a network between the two.
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