Depends on several factors in working in conjunction
Clock speed: The number of clock cycles (or pulses) generated per second by the computer.
(i.e. 900 MHZ = 900 Million pulses per sec,
2 GHz = 2 billion pulses per second).
Allows more instructions to be Fetched, Decoded and Executed making your programs run faster.
(See Fetch-Decode-Execute cycle)
Word Size: Number of bits a CPU can work on in any one clock cycle.
(i.e. The width of data; eg 8 bit, 16 bit, 32 bit, 64 bit even 128bit processors)
Bus Size: The internal circuits (or highways) that move data around the system can also have different widths
A Data Bus and Address Bus that carry more data each clock cycle,
will make the CPU appear to work faster.
An address bus 8 bits x 8 bits could address 256 differnt RAM locations each cycle (28),
An address bus 16 bits x 16 bits could address 25536 different RAM locations each cycle (216),
Materials: Better quality materials in the CPU have better relaibility, speed and performance.
The speed of the slowest component may slow the whole machine down
(i.e. a botttleneck).
Architecture:
The design of the CPU and the computer can affect the performance