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RISC and CISC and INTEL Pentium

Posted on 2002-04-22
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- what is RISC and CISC ?
- What is difference between Pentium 3 and RISC or CISC
in the aspect
of the speed , performance , reliable ??

- I heard that SUN uses RISC processor. Is that right ? and what about HP-UX ?

- Does anyone know the speed comparison between RISC in UNIX and Pentium at any frequency ( MHz ) ?

- If Pentium processor family at very high speed such as pentium four , is faster than RISC processor( in Sun or anything else ) then, why don't we use Pentium 4 to be the SERVER.??

- What is Flash Ram ?? Is it different from Ram on Personal Computer such as 128 Mbytes on My computer ? If so , what is the difference between these ?

Thanks very much in advances.
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Question by:leumas
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by:magarity
ID: 6960869
Looks like you're a little confused here.  RISC and CISC stand for 'Reduced' versus 'Complex' Instruction Set Computing'.  It is a style of microprocessor architecture.  

Neither is a brand or model name so the comparisions you ask for do not exist.

As example, Intel PC microprocessors (called x86) and Motorolla processors are CISC whereas processors like the Intel i860, DEC's ALPHA, and Sun's SPARC chips are RISC.

Flashram is just non-volitile memory.  When the power is turned off, it does not lose the information stored in it.
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by:jhance
ID: 6960902
>>- Does anyone know the speed comparison between RISC in UNIX and Pentium at any frequency ( MHz ) ?


That would be a meaningless comparison.  It's like trying to compare pickup truck vs. single-engine aircraft.  There are few similarities beyond both being transportation equipment.

RISC vs. CISC is more a religious issue than anything.  In the beginning of RISC, it was the beat-all/end-all.  But it didn't turn out that way.  In fact, RISC developed many new ideas such as pipelining, multiple-execution units, prefetch queues, branch prediction, to name just a few.  What has happened is that CISC processor designers found that RISC techniques worked well in CISC designs also. So what you have today is a blurring between what is and is not RISC or CISC.  The most advanced CISC CPU today, the P4 looks as much like RISC as it does CISC.  The most advanced RISC chips of today (like the SUN SPARC, MIPS, or Intel ITANIUM) look very CISC like.  There are few pure-RISC commercial  processors out there now, I'd say the HP PA-RISC is among the most "RISC" out there in the commercial market, or perhaps the ARM or RISC CPUs found in Windows CE based handhelds.
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magarity earned 50 total points
ID: 6963377
This should help:  Here is an exaggerated explaination of the difference between RISC and CISC:

RISC processor:
Engineers say:  "We want our chip to be as simple as possible.  If anyone wants to do multiple operations, they'll just have to use program loops."
Instruction #1: Add two numbers together
Instruction #2: Multiply two numbers together

CISC processor:
Instruction #1 and #2 same as RISC processor.
Engineers say: "Our user demographic will often run programs that need to multiply five numbers.  Rather than make them do instruction #2 four times, we'll have a special instruction.
Instruction #3: Multiply five numbers together

The thing is, when do you stop once you start down the CISC path?  There are the MMX (Intel) and 3DNow! (AMD) intructions for doing operations related to video.  These could all be done with basic arithemetic instructions but would take more cycles.  So the tradeoff is a more complicated chip that can do all kinds of instructions versus a simpler chip that can do everything but just takes more cycles to perform really complex operations.

If I have a PC playing a 3D video game, I want special instructions so the CPU can be as quick as possible to do the strange calculations 3D graphics require.  On the down side, it is big, expensive, and hot.  Also, because of all the miscellany instructions, the thing is actually SLOWER to do something really basic, like add two numbers together.  Has to sort past all the MMX and whatnot instructions.

If I have a server and all it does it fetch files from the hard drive and send the data out the network card, that's not so complex.  About the hardest thing the server has to do is check to see if user X has permission to read file Y.  This CPU should be as simple as possible, see?  Really expensive hard drive RAID controller cards have RISC CPUs on them because all they have to do are a few basic calculations as fast as possible with no fluff like MMX.  

So you see, RISC and CISC are for wildly different jobs and can't be easily compared.
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by:leumas
ID: 6978005
Thanks so much.
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