820 is a part number go to
Laptop, Notebook, Desktop, Server and Embedded Processor Technology - Intel for information.
what is a CPU Ghz, Ghz = 1 billion Hertz, ( 1,000,000,000 )
or cycles per second in simpler terms.The bigger the number the faster it can execute a set of instructions.
Slower speed CPU's will take long to execute the same set of instructions.
Also CPU speed is only one part that determines the speed of a computer.
Other factors like
FSB ( Front side Bus )
How much memory ( L2 and DDR )
Hard drive speed