The CPU, or processor, is the nerve center of the computer system. It is the component that processes all of the data within the machine. The type of CPU should be the first decision made when building or updating a computer system. Important factors when selecting a CPU are the processor speed and bus speed.
Processor Speed
• Processor speed measures how fast a CPU cycles information. It is generally measured in MHz or GHz. The higher the speed the faster the performance. Faster processors consume more power and create more heat than their slower counterparts. For this reason, mobile devices, such as laptop computers, typically use processors that are slower and consume less power in order to extend the time they can operate using batteries.

Bus Speed
• CPUs transfer data between various types of memory on the system board during its operation. The pathway for this movement of data is called the bus. In general, the faster the bus, the faster the computer will be.
• When selecting a CPU, keep in mind that applications continue to evolve.
Purchasing a CPU of moderate speed may satisfy current requirements.
Future applications, however, may be more complicated and require, for example, fast high resolution graphics; if the CPU is not sufficiently fast, the overall performance, measured in terms of response time, will be slower.
• The CPU is mounted through a socket on the motherboard and is normally the largest component on the board. The motherboard must be equipped with a compatible socket to accept the selected CPU.
RAM
• RAM is a type of data storage used in computers. It is used to store programs and data while being processed by the CPU. Stored data is accessed in any order, or at random, as needed. All computer programs run from RAM. Besides the CPU, the amount of RAM is the most important factor in computer performance.

- Every operating system requires a minimal amount of RAM in order for the OS to function. Most computers are capable of running multiple applications simultaneously, or multi-tasking. For example, many users run email programs, Instant Messenger clients, as well as anti-virus tools
or firewall software. All of these applications require memory. The more applications that need to run simultaneously, the more RAM required.