Power 7 CPU - 8 cores

[minator]

Any CPU engineer will tell you instantly we have hit the wall and all this multi-core desktop CPU stuff is just a scam really. The maximum number of cores without losing efficiency of code execution is effectively 3. Not 4 not 8 but 3. You can not utilise much more than this without actually starting to waste cycles of CPU time delaying/setting up use of threads to run on other cores.

Apparently the GPU guys didn't get that memo. top end GPUs run half a million threads on hundreds of cores in parallel.


Building faster single threaded CPUs is getting more and more difficult.

The 5GHz variant of the Pentium 4 was cancelled because it was going to use 150W.  They went to a more efficient design with multiple cores after that because it is far more power efficient.

Even mobile phones are quad core these days.  Expect to get a lot more cores in the future.

[minator]

PS4 is most likely x86 according to the rumours.

But it wont be *just* x86.

Their CTO mentioned what it has very vague terms in a speech.  If there's an x86 in there it'll just be one of many processors.

I took it to mean PS4 will be  x86 + Cell + GPU, with an FPGA thrown in for good measure.


XBox 720 is said to have a 16 core CPU that IBM designed but no one seems to know what the cores are.  According to a leaked Microsoft doc they could be x86 or ARM.


Wii U is supposed to have 3 PPC cores supposedly based on the POWER7 cores.

[minator]

ARM has a simple decoder and consumes very little electricity but the integer CPU could be more powerful. x86 is more powerful but has a very complex decoder wasting electricity. The 68k would fit in between with a moderately complex decoder but is similar in integer performance, if not better than x86 (assuming basic enhancements like in 68kF and no 64 bit for low power target). While consuming more electricity than ARM, the 68k has the best code density which helps performance and allows for a smaller memory footprint. The 68060 was pretty low power consumption for it's performance and time.

As I understand it the 68K was running into difficulties when it was getting to things like the 68060.  That was one of the reasons they abandoned it.

Having a complex and powerful ISA might be wonderful from the programmer point of view but it's most likely the opposite from the hardware designer's point of view.  Someone has to implement all those commands in hardware and this can lead to some very tricky situations.

e.g.  What happens if your processor is doing some complex operation and an interrupt comes in?  Do you hold the interrupt and keep going?  What if the operation takes a long time involves reading from RAM?  You probably can't wait that long so you have to find a way of halting the processor, storing the state mid instruction, handling the interrupt, recovering the state and restarting where you left off.

Thats the sort of problem the hardware designers have to deal with.  Then you have to build it and test it, including that particular behaviour.  There's a reason no one but IBM and Intel use CISC these days - and they both tried to get rid of it.

[minator]

There's a big, big difference between massive multicore in special-purpose applications, and massive multicore for general-purpose computing, though.

I know, that why I mentioned single threaded next :-)

Graphics in particular is a task that's pretty much tailor-made for massive parallelism.

Yup.

Word processors, file managers, and other unglamorous productivity software? Not so much.

True, but it's now got to the point that a lot of software doesn't require a high end processor anyway.

On the other hand a lot of the stuff that does require high end processors can be parallelised.  I just bought a new high end laptop with a quad core CPU because I run things that can max it out - video editing, recording music and photo editing.

These can all run across multiple cores.  That said, editing 22 Mpixel images appears will happily use all 8 hardware threads but it seems to be more limited by the hard disk (which is actually a s**t hot fast SDD).

[/QUOTE]web browsers[/QUOTE]

Actually these do quite a lot at the some time so they can take advantage of multiple processors.

[minator]

Indeed; everybody wants to ride the hot new ARM wave that's surely going to last forever, and nobody seems to remember when the new wave was PPC...

Because they're cheap and made in vast quantities - much, much higher than x86.

But the real reason:


Go to eBay and search for "Android Laptop 10", buy it now only.
10" laptop for £80 (including postage) that's faster than any of the Sam boards.

That's why.

Welcome to the world of ultra low cost computing.

[minator]

Speed of light. If a signal can't get from one end of the chip to the other in a clock cycle

This problem was encountered and fixed years ago.  IIRC the Pentium 4 was suspected to have pipeline stages just for moving things around.