CISC vs RISC

[revenuee]

I've been trying to do some research on this topic and as much as i understand the differences between the two i still have a question of implementation.

Are current PPC's in apples computers using RISC, and all others like Intel and AMD using CISC?

or it is arbitrary to use those terms anymore, is there a new system.

 

[bousozoku]

RISC and CISC have taken on new meanings in recent years.

RISC used to mean Reduced Instruction Set Computing, but lately, RISC processors have nearly as many instructions as the CISC processors used to have. More so now, it means that the majority of available instructions can be performed in one or two clock cycles, rather than the 5 or 6 of traditional CISC. The PowerPC line fits into this description quite well. With AltiVec, it handles many instructions.

CISC processors still have many instructions, but more of them require less time to process. The processors have taken on other RISC characteristics as well. In fact, the Athlon processors from AMD have always been RISC processors emulating CISC x86 processors.

 

[acj]

Just remember two things: RISC is better. CISC is better.

 

[Makosuke]

Like bousozouku said, there has been a lot of conversion between the two as they relate to PPC and x86 processors recently. At this point, though PPCs are "more RISCy" and Intel's chips (the P4/Xeon series, anyway) are "more CISCy", it's not exactly accurate to put either label on either line of processors.

You could probably say that things have probably gone toward a RISC-style core with higher-level CISC-style instruction set (or instructions that make use of seperate computation engines on the same chip, ala AltiVec), which seems to be the most efficient way of going about things.

So far as I know, the same is pretty much true of most modern high-end procecssors; they all use some of both worlds, so it's more of a continuum than any sort of hard division.

Not that you couldn't still have a "real" RISC or CISC chip, just most aren't (and of course even those divisions aren't defined in terms of hard numbers, they're just design philosophies).

 

[Catfish_Man]

For an example of a "real" RISC chip, look at the now dead and much mourned Alpha chip series (made by DEC, then Compaq). For a real CISC chip (afaik) try an Intel 80286 or a Motorola 68xxx. Current chips are (as said above) really hybrids, with x86 chips breaking down instructions to be more RISC like, and PowerPC chips adding instructions (Altivec, for example) to be more CISC like. There's also VLIW, which is much newer, and different from either CISC or RISC. The only VLIW chips I know of are Sun's MAJC, Intel's Itanium, and Transmeta's Crusoe.

 

[revenuee]

Okay... thanks for the posts guys. I remember when i did look into this a few years pack it was a defined line, as many of you said. As i was looking into it a few days i found that i got a lot of the same information i got years ago, and didn't really find a whole lot for the new generation of processors.

Now i know why it's never really talked about anymore.

Again thanks ... i'm going to look some more into this VLIW chip

 

[bousozoku]

Originally posted by Catfish_Man

...
There's also VLIW, which is much newer, and different from either CISC or RISC. The only VLIW chips I know of are Sun's MAJC, Intel's Itanium, and Transmeta's Crusoe.

I think you should also claim HP's Precision Architecture as the original commerical VLIW processor. It is the progenitor of the Itanium line.

 

[Catfish_Man]

Originally posted by bousozoku
I think you should also claim HP's Precision Architecture as the original commerical VLIW processor. It is the progenitor of the Itanium line.

Yeah, I'd forgotten about those.

 

[hvfsl]

The three main chips in the world (Pentium, Athlon and PPC) are all a mixture of CISC and RISC now. The P4 and the Athlon have a RISC core, but a converter to convert the instructions back into CISC. The PPC is still mainly a RISC chip, but it has a lot of the features of CISC chips in it.

This is why AMD could have made PPC chips for Apple, since they already have RISC chips, this is where some of the rumors about Apple and AMD chame from.

 

[daveL]

Originally posted by bousozoku
I think you should also claim HP's Precision Architecture as the original commerical VLIW processor. It is the progenitor of the Itanium line.

I do not believe that is correct. HP's PA cpus are RISC, not VLIW. Itanium was/is a joint development between HP and Intel to develop VLIW processor architecture.

 

[Bear]

Originally posted by hvfsl
...
This is why AMD could have made PPC chips for Apple, since they already have RISC chips, this is where some of the rumors about Apple and AMD chame from.

This is nonsense. Intel could just as eaily produce a PPC chip. All they neeed are the designs for it.

Just because two chips are RISC based, it doesn't make them similar. The instruction sets could be way different and still b oth be RISC chips.

Yes AMD could have manufactured the PPC chips, but who would have given them the design?