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CPU - Central Processing Unit
by John Anthony


The central processor unit (CPU), often called just the 'processor', is the heart of the PC. It controls everything that happens in the computer and it's overall performance is determined by a number of factors:
  • number of cores
  • clock speed
  • types of caches

A core is an independent processing unit. Early CPUs were single core. As chip geometries shrank and more circuitry could be fit on them, dual core processors became available. This allowed each core to process instructions simultaneously resulting in higher performance. Currently some CPUs have 4, 6 and even 8 cores.

Clock speed is measured in Ghz (billions of clock cycles per second) and is a measure of how fast the CPU can process and execute instructions. The faster the clock the higher the CPU performance.

Cache is a small very fast memory that the processor uses frequently. It is located close to the CPU which enables the CPU to store and retrieve frequently used data, much faster than it can from DRAM memory.

As CPUs evolved different levels of cache were made available to the CPU

L1 caches were the first to appear. They are the smallest and fastest type.
L2 is larger with less speed than an L1 cache.
L3 is the largest and slowest of the cache types.

However, all caches are much faster than DRAM memory.

Intel processors

The Intel Pentium class of processors are the most popular type found in PCs, and are offered in a many versions:

The Celeron is an entry level processor. It is really a Pentium 4 that runs at a slower clock speed and uses a smaller L2 cache. A smaller L2 cache guarantees more overall cache misses which results in lower performance.

A Pentium 4 runs at it's full rated speed and uses a large L2 cache.

The Intel Pentium Dual Core released in 2006 had dual cores which gave it a significant over it's single core predecessors.

The I3, I5 and I7 are the latest in the Intel CPU line. THey all are offered in multiple, high clock speed cores and large L1, L2 and L3 caches.

AMD processors

The chief competitor for Intel is AMD (Advanced Micro Devices). They have approximately 25% of the market.

They make a number of processors: Sempron, Athlon and Phenom. The Sempron is a single core processor which competes with early Pentium processors. The Athlon and Phenom are offered in higher performance architectures with multiple cores and caches.

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