xbox 360 cpu vs pc cpus

I heard that xbox 360 has a 3 core 3.2 ghz processor which sounds way too high tech for the last quarter of 2005.. what are its flaws?

marketpantry said:

I heard that xbox 360 has a 3 core 3.2 ghz processor which sounds way too high tech for the last quarter of 2005.. what are its flaws?

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IBM made the deal to make that CPU in 2003. You're right, that does sound way too high a technology for that time frame! I'd like to know the answer as well.

-Collin-

IBM makes ultra High performance, super computer chips. Chips that make Neha look like a celeron. So naturally saying IBM couldn't make such a powerful chip in 2005 is not true. I don't know how it compares clock to clock as compared to AMD's/Intels CPU, but I believe it is less than AMD's chips (although I really don't know). The 360's CPU is based on a powerPC design, but that is about all I can say really, I don't know more about it.

Edit: also don't forget that each of those cores can hyperthread also.

My impression is that its not so powerful, it is a low cost product with a small number of transistors, and the really big disadvantage is that it uses in-order execution. In-order reduces die-size, power consumption and cost but reduces performance even more.
Hyperthreading (IBM call it Multithreading i think?) is almost a requirement for in-order CPUs since they will stall whenever waiting for data and the cores will then sit idle for long periods without it. Intel Atom has hyperthreading for the same reason.

Even the out-of-order powerPC processors was somewhat disappointing, Apple was working with IBM on the G5 and had big plans for it, and we all know Apple only made a few G5s and went to Intel instead since IBM could not give them acceptable performance per watt.

Dapman02 said:

IBM makes ultra High performance, super computer chips. Chips that make Neha look like a celeron. So naturally saying IBM couldn't make such a powerful chip in 2005 is not true. I don't know how it compares clock to clock as compared to AMD's/Intels CPU, but I believe it is less than AMD's chips (although I really don't know). The 360's CPU is based on a powerPC design, but that is about all I can say really, I don't know more about it.

Edit: also don't forget that each of those cores can hyperthread also.

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I don't get it. If IBM made such good CPUs, then why don't we see them dominating the CPU industry?

PPC6 was a big leap though. Very nice gains per watt and very nice power from them.

th3 is correct about the cpu being cheap and not very powerful, but the design really mimic's PS3's in that it can do multiple executions at one time to save on latency, which the cell has a problem with too.

Blazing fire said:

I don't get it. If IBM made such good CPUs, then why don't we see them dominating the CPU industry?

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Because x86 is a terrible monster that won't die. If we were on a better arch than computers would be faster by now, simply because x86 is so limited now since we've basically pushed it beyond how long it was supposed to last.

maybe they think its easier to make money from the software side than hardware and only licensing their hardware R&D.
they also wouldn't have to invest billions in building and updating fabs.

Cheator said:

Because x86 is a terrible monster that won't die. If we were on a better arch than computers would be faster by now, simply because x86 is so limited now since we've basically pushed it beyond how long it was supposed to last.

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DavidJa said:

maybe they think its easier to make money from the software side than hardware and only licensing their hardware R&D.
they also wouldn't have to invest billions in building and updating fabs.

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I see your point but something does not add up yet. Let's not hijack the thread. I'll start a new one.

splat said:

http://en.wikipedia.org/wiki/Xbox_360_hardware#Central_processing_unit

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wait... this processor only has 1 meg cache? thats odd.... i also heard something about only being able to do 2 operations per core per cycle or something... isnt that also well under what the normal processors do?

I created the thread here: http://www.ocforums.com/showthread.php?t=588318

Blazing fire said:

I see your point but something does not add up yet. Let's not hijack the thread. I'll start a new one.

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Edit - added "IBM CPUs?"If IBM made such good CPUs, then why don't we see them dominating the CPU.""

Intel micro-architectures are much faster than the PPC micro-architecture present in the Xbox 360.


The Xbox 360 only has static branch predicition; this means each and every 'if' check, whether true or false, incurs a huge performance penalty as the machine waits for the pipeline to evaluate the branch. A 'virtual' function call is devastatingly slow.


The Xbox 360 has very few execution units; can't remember off the top of my head but I think it can execute 2 instructions per clock. If two threads are active on a single core, each thread is executing 1 instruction per clock. Hyper-threading allows one thread to use both execution ports when another thread stalls, which helps to eliminate the penalty.


The Xbox 360 does not perform out of order execution; it is up to the compiler to sequence instructions optimally.


The Xbox 360 instruction set is reduced-- based on the RISC instruction set, it generally requires more instructions to perform the same task as x86.


Hard to give even a rough estimate because it totally depends on the programmer, the compiler and computing task, but in general I'd say a single Xbox 360 thread thread is equivilent to ~1ghz Pentium III. Code that is perfectly optimized, however, is a completely different story.

What is the disadvantage and advantage of in-order execution and out of order execution?

Blazing fire said:

What is the disadvantage and advantage of in-order execution and out of order execution?

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Ordinarilly, the processor stalls whenever the results of a pipelined instruction must wait for the results from the previous instruction. Out of order execution allows other instructions to execute while waiting for those results. Hyper-threading expands this concept to allow another thread to execute if the current thread stalls for any reason.



Out of order execution is probably the single-best feature after the L1 cache you wouldn't want removed from a modern CPU. I'll take it over branch prediction any day Its primarily what made the Pentium Pro so special!

Hey nanerbeet, why don't you join the discussion in this thread?

How come the Xbox 360 does so well in games and my vary expensive comparative pc cant run all games like a Xbox 360 can.

We all think that just because we have the supposedly newest cutting edge cpu's and such technology that we can get from the egg and other places that we are on top of things. NOTTTT. We are are at least 2 to 3 years behind from what the government has had at there disposal for so long that it would make your head spin.

wingman99 said:

How come the Xbox 360 does so well in games

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All console games are made to run on only one set of hardware. They can test it and change the code accordingly to get that perfect frame rate under all circumstances. However, with a PC, you can be running any type of operating system, all operating differently, and not only tons of generations of video cards, but also video cards from numerous manufacturers.

You can optimize the game for a certain console, but you can't optimize code for "all operating systems", and "all hardware".

Apples and oranges regarding the power of the triple core CPU. Intel has a dual core 1.2Ghz processor for hard drive controllers, supports something like 4GB of RAM too... but that doesn't mean you could run your system with it.

lokie said:

We all think that just because we have the supposedly newest cutting edge cpu's and such technology that we can get from the egg and other places that we are on top of things. NOTTTT. We are are at least 2 to 3 years behind from what the government has had at there disposal for so long that it would make your head spin.

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You mean servers where they put multiple CPUs together?