Monday, November 28, 2011

Know the Specs: CPU

Do you know all there is about the cpu?

Ok, so im starting a new series called 'know the specs'. Reason being is that there are tons of high end system components that are so similar, it comes down to commonly overlooked specifications to decide which one is better.
To start off, im going to cover the cpu, however this series will go beyond just computers and go into speakers, screens, and other daily appliances.

Ok, so off to a (hopefully) good start. I feel that I explained the goal of this without sounding too verbose. Hopefully I can say the same about what is to follow…

Common specifications:
  • Clock speed (measured in Ghz): this is the speed that the processor can process data.
  • Cores: how many processing units there are in the CPU. More cores allow more multitasking, but not an increase in speed per core.  
  • Socket: This refers to the layout of pins on the bottom of the cpu. The socket on the cpu and motherboard must mach.
Uncommon specifications:
  • Hyper transport (most common on AMD processors): in short, hyper transport allows data to be sent on the rising and falling clock signal, this allows for higher latency. AMD uses hyper transport instead of a front side bus.
  • L2 cache memory: L2 cache is per core memory, meaning that if you have 4 cores, each core will have its own L2 cache. This memory is much faster than ram, and is used for on the fly data calculations. Try to avoid processors with low L2 cache, or that share L2 cache between multiple cores.
  • L3 cache: L3 is similar to L2, but is shared between all the cores on the processor. Its most practical application is to act as a buffer between the L2 memory and the cache.
When buying a CPU, the first thing to look for is its speed. The higher the Ghz the better. After that, look at how many cores it has. After that, factor in the L2 cache, followed by front side bus / hyper transport speed.


Sub-Radar-Mike said...

Hmm, well today I learned about L2 caches, thanks.

minecraft129 said...

interesting, I didn't know what a cache was, maybe ill be sure to look for L3 cache in a few years.

Edward said...

I will keep this in mind.

M Fawful said...

Great summary. I always wondered about what L2 cache was and why i should care.

river-wind said...

L2 cache existed before multi-core processors, originally being the first level of cache on the motherboard instead on the CPU itself. Since ~2001 more and more chips moved L2 cache onto the CPU itself ('on-die'), and then many moved L3 on-die as well. Often these days, L2 cache somewhat correlates to cpu cores, but not in the way suggested. Some CPUs may have L1 and L2 cache per core, and also a shared L2 'unified' cache to assist with managing concurrency and reducing latency in multi-threaded applications (programs designed to run different parts of the program in parallel on different cores/CPUs - like a game that handles player input on Core 1, enemy AI processing on core 2, physics on core three, and sound on core 4).

L1 to L3 cache is simply a multi-level attempt at balancing processing speed and cost. L1 is the fasted memory, but it's expensive, so it's small. General overview: If some data X is used by the CPU, it's placed into L1 in case it's needed again right away - getting it back will be really fast. If other data is used and that data item X isn't seen as important, it gets moved to L2, a slightly larger, slightly slower, slightly cheaper memory bank which is physically farther out than L1 (more latency/takes more time for the electrons to travel to the ALU (Arithmetic Logic Unit)). L3 is bigger and slower still, and the next level down. After than, your RAM/machine memory, which is the super-cheap-so-let's-have-gobs-of-it level cache. After that, the Hard drive itself acts as the final storage location for the data; everything between the HD and the CPU is working memory.

Publius said...

glad you explained this, you made it so clear!

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