CPU stands for "Central Processing Unit". This is also known as a processor. This is the piece that most closely reflects the speed of the machine. The speed of the processor is measured in megahertz, or gigahertz (1,000 megahertz). The faster the processor, the faster the machine in general. This is not the only indicator of speed in a machine, however.

When purchasing a laptop there are two major vendors that provide processors. The first and largest distributor is Intel, who manufactures the Pentium and Celeron series processors. The second distributor is AMD who manufactures the Athlon and Duron processors. Each company measures their speeds differently. Intel traditionally names their processors after the speed of the processor. For example, an Intel® Pentium® 4 2.80GHz Processor runs at 2,800 megahertz, or 2.8 gigahertz. AMD names their processors after the equivalent speed of the Intel processors. For example, an Athlon XP 2800+ Processor runs at the equivalent of a 2.8 Ghz Pentium processor. The actual speed of the AMD processors are lower than the Pentium equivalents, however the performance remains the same. This is due to different design and manufacturing techniques.

Additionally, Intel and AMD's budget line processors, the Celeron and Duron respectively do not have the same performance as the Pentium and Athlon processors. The reason for this is the elimination of the expensive L1 and L2 cache, or memory that delivers data quickly to the processor. The budget line processors will always perform slower than the performance line.