|02 Apr 2011||#1|
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CPU Consideration Factors
Some CPU consideration factors and points.
The raw speed of a CPU should be taken into consideration alongside other factors. These are the number of cores, the number of cache(s) and their size(s) and their internal pipeline architecture (differences between Intel and AMD).
CPUs process, or crunch, data that is supplied to it from the system RAM. In comparison to the internal speed of a CPU, the RAM is slow. In order to mitigate this, the CPU has a number of caches built-in to the die. Although the caches run slower than the core of the CPU itself, they are nonetheless faster than the system RAM and can therefore be more quickly accessed.
Let's use an analogy here: Reading a book. To start off with, there are no books and all books need to be bought/borrowed from a shop/library. This is akin to powering up your system. All the CPU data needs to be fetched from RAM. After a short period of running, the caches are populated and, providing the required data is in one of the caches, data access is much quicker. In our book analogy, the cache levels can be thought of as follows: Level 1 is the desk at which you are sat, Level 2 is a bookcase in the same room, and Level 3 is a bookcase in another room. The RAM is the shop/library from where the books originate. As you can see, it is much quicker to access data from the caches (although they get progressively slower from L1 to L2 to L3) than it is from RAM.
Taking all of this into account, we can see that everything needs to be considered together. It is possible for a processor with a slower clock speed to actually be quicker than one with a faster clock speed. For example, consider my old and new processors (both dual-core):
Old: AMD Athlon X2 6000+ @3.0GHz = 2000SBS
New: AMD Athlon X2 7550 @2.5GHz = 3600SBS
Where SBS = System Bus Speed in MHz. As you can see, despite a decrease in core frequency of 500MHz, there is actually a performance increase of 80% in a theoretical ideal situation (real-life situations may give differing performances).
Here is a comparison chart (from AMD) showing this information: Compare AMD Processors for Desktops: AMD Athlon X2 7550 and AMD Athlon X2 6000+
As you can see from this, the main difference (apart from the clock speed) is the number and sizes of the caches. Both L1 caches are identical, whereas the L2 cache is halved for the new CPU compared with the old one. However, this is more than made up with by the addition of a third cache, L3.
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