Even though today's processors are tremendously fast, their performance can be affected by a number of factors:
CPU clocks can sometimes be sped up slightly by the user. This process is known as overclocking. The more pulses per second, the more fetch-decode-execute cycles that can be performed and the more instructions that are processed in a given space of time. Overclocking can cause long term damage to the CPU as it is working harder and producing more heat.
The bigger its cache, the less time a processor has to wait for instructions to be fetched.
A processing unit within a CPU is known as a core. Each core is capable of fetching, decoding and executing its own instructions.
The more cores a CPU has, the greater the number of instructions it can process in a given space of time. Many modern CPUs are dual (two) or quad (four) core processors. This provides vastly superior processing power.