What effects a CPU's performance?

Number of cores:

Theoretically, a CPU with more cores is able to run multiple processes at the same time. Although some code might not be able to use this to full effect.

Clock Speed

The number of operations ran a second, higher clock speed means more instructions. Measures in Hertz(samples per second). Most computers have 2-4Ghz

Cache Size

Cache size is memory that the CPU is able to quickly access compared to RAM. Its used for common instructions which increases speed.
There are multiple levels of cache, getting bigger the slower it is.

Clockspeed 2Ghz 2.5Ghz 3Ghz 3.5Ghz 4Ghz

Number of Cores 1 2 3 4

(Theoretical) instructions speed: Ghz

Pipelining

A technique used by alot of CPUs to increase performance. Without pipelining, a processor will fetch an instruction, decode and then execute it. Then do the next instruction.
With pipelining, the processor will fetch an instruction, while executing an instruction at the same time. This improves performance but can lead to glitches when an instruction needs the data of an instruction that is still in the processor. Therefore that instruction needs to be redone which is inneficient.