When the computer receives information, it is processed by the central processing unit or CPU. The CPU is aided by two kinds of memory, RAM and ROM.
The CPU
The CPU is made up of tiny electrical components all put together on a microchip. This is called the microprocessor. The microprocessor is housed on the circuit board or "mother board" inside the computer. The CPU manipulates and processes data which it receives in digital form from an input device. All computers have a CPU, but not all CPUs are compatible with all computers.
Two major manufacturers of microprocessors are Intel and Motorola. Intel CPUs are used in IBM compatible computers while Motorola CPUs are used in Macintosh computers. The Intel microprocessor cannot usually run a program written for a Motorola CPU and vice versa. Therefore these two types of CPUs are not interchangable.
Another area in which processors differ is in speed. New ways are continually being sought to increase the speed of the microprocessor, and microprocessors today are many times faster than the early models. One of Intel's early microprocessors was the 80286, released in 1982. Commonly called the 286, it was a 16-bit processor with a 16-bit data bus. This means it could process and transfer two bytes of information at a time. The 386 is a 32-bit system which means it can handle twice as much data as the 286 at a time. The 486, introduced in 1989, added other features to the 386 to make it even faster. Today the Pentium processor is roughly five times as fast as the 486. Motorola has its own line of comparable processors such as the 68020, 68030, and 68040.
Though the CPU processes data, it does not have much room to hold information. It therefore relies on two types of memory: RAM and ROM.
When the power switch is flipped on, the computer needs to be told what to do. This information is stored in small chips called read-only memory or ROM. It tells the computer to look for things like an operating system. The information in ROM is always there even when the computer is switched off. This is called non-volatile memory. Thus the instructions can be read right away, and the information in ROM can never be changed.
Another kind of memory is random-access memory or RAM. RAM chips contain programs and data, and are known as volatile memory; they lose their contents when the computer is switched off. The CPU contacts RAM whenever it needs to look something up, and the more RAM on the computer, the bigger the program it can hold, and the faster it can run the program.
Introduction to Computers
IHC - 2E03
Humanities Computing Centre