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RISC vs. CISC: What's the Difference?

48 点作者 pathompong将近 10 年前

8 条评论

struct将近 10 年前
I don&#x27;t have access to the actual paper, but looking at the linked results[0]:<p><pre><code> Core Name Performance (MIPS) Energy (J) Power (W) Cortex A8 178 25 0.8 Cortex A9 625 11 1.5 Atom N450 978 16 2.5 i7-2700 6089 28 25.5 </code></pre> So A9 delivers 625&#x2F;1.5 = 417 MIPS per Watt, whereas the i7 delivers 6089&#x2F;25.5 = 239 MIPS per Watt and the Atom delivers 391 MIPS per Watt.<p>In addition, their spreadsheet has an &quot;energy&quot; tab calculated from a &quot;normalized&quot; power figure (where Atom comes out on top), but if you multiply the measured figures without the dubious adjustment, it seems that the A9 is actually more efficient (at least when you consider the board power), and MIPS is conspicuously absent from this spreadsheet. So the fundamental conclusion is &quot;either ARM or Intel are better, but it depends on what you measure under what workload&quot;.<p>[0] <a href="http:&#x2F;&#x2F;research.cs.wisc.edu&#x2F;vertical&#x2F;wiki&#x2F;index.php&#x2F;Isa-power-struggles&#x2F;Isa-power-struggles" rel="nofollow">http:&#x2F;&#x2F;research.cs.wisc.edu&#x2F;vertical&#x2F;wiki&#x2F;index.php&#x2F;Isa-powe...</a>
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Symmetry将近 10 年前
ARM up until the 64 bit transition was always one of the CISCiest RISC designs and x86 wasn&#x27;t nearly as CISCy as, say, VAX. 64 bit ARM is a much more traditional RISC ISA than the previous encoding.<p>But anyways, here&#x27;s the link I always post when people talk about RISC versus CISC. <a href="http:&#x2F;&#x2F;userpages.umbc.edu&#x2F;~vijay&#x2F;mashey.on.risc.html" rel="nofollow">http:&#x2F;&#x2F;userpages.umbc.edu&#x2F;~vijay&#x2F;mashey.on.risc.html</a>
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JoachimS将近 10 年前
None of the CPUs compared have very reduced (as in few) number of instructions. We&#x27;ve come quite far from MIPS1, IBM 801 and the first SPARCs in terms of ISA complexity.<p>The big difference is really that x86 has an ISA-&gt;uop decoder, which basically is another decoder in front of the decoder in a RISC.
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TheLoneWolfling将近 10 年前
My thoughts on the matter:<p>Given that process sizes keep shrinking, and every time you shrink the process size you can fit more on the chip, and heat doesn&#x27;t scale (as in, the smaller the process size the more heat per in^2), and we&#x27;re up against a heat wall as it is, we&#x27;re to the point now where a large chunk of the chip <i>has</i> to be dark at any point in time. As such, CISCs are looking better and better. Because you cannot really scale frequency more (due to heat concerns - freq^2 heat output, to a first approximation), and you have to run most of the chip dark at a time <i>anyways</i>, and you have the space, so you may as well have things that are optimized for rare use cases. And we&#x27;re already seeing that. The micro-ops on modern x86 processors are getting more and more complex and specialized.<p>This will especially start happening once we get decent CPU caches - the 3d-ish stacks that are being talked about. Where you have a separate chip stacked under or over the CPU that has a process optimized for RAM.<p>Note that this is <i>not</i> talking about ISAs, this is talking about the processor itself. Although it&#x27;s not done much currently, you can just as easily (or rather, with just as much effort) convert a RISC into CISC-like micro-ops (macro-ops?) as convert a CISC into RISC-like micro-ops. It&#x27;s looking more and more as though ISAs can be successfully decoupled from the actual processor design. Which is encouraging. Treat the instruction encoding as effectively a compression scheme for the instructions that the actual processor runs.
m0skit0将近 10 年前
IMHO author is actually missing the point of RISC architecture: instruction homogeneity allows for a simpler (and cheaper) hardware. Of course for software developers RISC or CISC, it actually doesn&#x27;t matter, that&#x27;s what abstract layers are all about.
SixSigma将近 10 年前
Headline : X found to be Y<p>&quot;X is Y&quot; as an assertion<p>&quot;or that&#x27;s what researchers claim in new report&quot; as a caveat<p>I hate this style
higherpurpose将近 10 年前
In other words, even if the x86 ISA itself is not bloated anymore, the CPUs <i>can be</i>. Because x86 CPUs still support a lot of 20-year old legacy stuff.
VLM将近 10 年前
Hundreds of MIPS is interesting, for a certain class of application, but it would be interesting to see the results for sub MIP applications. The microcontroller in a microwave oven.