System Performance and System Resources
The performance of a computer system depends upon how the system uses and
allocates its resources. Monitor your system's performance regularly so that you know how
it behaves under normal conditions. You should have a good idea of what
to expect, and be able to recognize a problem when it occurs. 
System resources that affect performance are described in the following table.
System Resource  | 
Description  | 
Central processing
unit (CPU)  | 
The CPU processes instructions by fetching instructions from memory and executing them.
  | 
Input/output (I/O) devices  | 
I/O devices transfer information into and out of the computer.
Such a device could be a terminal and keyboard, a disk drive, or
a printer.   | 
Memory  | 
Physical (or main) memory is the amount of random access
memory (RAM) on the system.   | 
Chapter 13, Monitoring System Performance (Tasks) describes the tools that display statistics about the system's activity and performance.