Written by James Newcomb
Tuesday May 5, 2009
Page 2 of 5

All Computers are not created equal - CPUs

When I talk about different performance levels for different price points I'm not just talking about the advertised speed, this is where the knowledge of the "specs within the specs" really starts to show its worth. As you probably already know, computer processors (CPUs) come in a variety of speeds, which everyone refers to as a number, in Gigahertz (GHz.) A 3.0 GHz. processor is faster than a 2.8 GHz. processor, which is faster than a 2.6 GHz. processor - or is it?

One thing you never see as an advertised CPU spec is cache (pronounced "cash") RAM. If you've never heard of cache RAM then my point should be becoming more clear. Cache RAM is a type of memory that's built right on the CPU. Most CPUs have at least Level 1 and Level 2 cache, and the newest breeds of processors now have Level 3 cache. The general Rule of Thumb is that the more cache RAM you have, the better your CPU is going to perform.

The cache RAM's job is to temporarily store previously used system memory information. Because the cache RAM is on the CPU, it's much faster to read that data from cache RAM as opposed to reading it from system RAM.

There are some processors that fail certain cache RAM tests at the factory, but are still partially functional. Instead of scrapping the whole CPU, they simply disable the defective cache RAM and sell it as a different product. While these items did fail certain quality tests, they are still completely usable products, but it is important to know whether you are getting a fully functional CPU the way it was designed to run, or if you are getting a partially diabled CPU that, while it will run fine, it's not running at the speed at which it was designed.

Another factor in processor performance is how many cores are on the CPU. Multi-core processors out-perform single-core processors in every way, as long as we're comparing similar speeds (a 2.8 GHz. dual-core processor can in most cases out-perform a 3.0 GHz. single core processor in cpu-intensive programs). The reason for this is that with a single-core CPU, it has to do all the work by itself. With a multi-core processor, one core can handle things such as running Windows and other simple tasks, while the other core(s) can take on different tasks, without having an effect on the performance of the work that the other processor is doing.

Much like CPUs with defective cache RAM, manufacturers will sometimes find a multi-core processor that has failed tests on a particular core. AMD now has a processor family called the Phenom II, which has a triple-core processor. This triple-core processor is a quad-core chip that has failed some tests on one of the cores, so they disable it at the factory. While this CPU is not running at it's optimum speed per the design, there is a nice advantage to this particular processor type.

Let's take an AMD Phenom II X4 processor running at 2.8 GHz. per core for an example. This CPU has 4 CPU cores, it consumes 125 Watts of power, and has 6 MB of Level 3 (L3) cache RAM that is shared across all four cores. If this CPU fails tests on a core and they disable it, it now becomes a Phenom II X3 processor. Because this CPU has a core disabled, it now consumes 25% less power, so it's now only using 95 Watts of power, which means it will create less heat. Since the L3 cache RAM is shared across all cores, we now extend the 6MB to 3 cores instead of 4 which increases the cache per core from 1.5 MB to 2 MB. As I said earlier in this article, the more cache RAM the better!

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