System Bus

RAM

CPU

Input

Output

InstructionDecoder

Register

Control Unit

Arithmetic Logic Unit

Central Processing Unit

In order to work, a computer needs some sort of "brain" to perform its calculations and

interact with other peripherals. A central processing unit (CPU) is the “brain”of the computer

which reads and executes program instructions, performs calculations, and makes decisions.

We call it the central processing unit because for the word “central”, the CPU is the centre of

data processing; for the word “processing”, it is a processor that processes(move and

calculates) data; for the word “unit”, it is a chip which contains integrated chips and million

of transistors. A CPU can tell the rest of the computer system what to do, and also performs

calculation and manipulates data. There are two main components in the CPU. One is control

unit, and another one is arithmetic logic unit.

Like the name implies, the control unit controls the entire computer system to carry out

stored program instructions. Arithmetic logic unit (ALU) is a circuit in the CPU where to

perform arithmetic (addition, subtraction, multiplication & division) and logic operations

(equal or larger). The CPU operates in four steps: fetch, decode, execute, and writeback.

(Wikipedia)

The first step fetch is to gather information from memory. The instruction register (IR)

works here. It is a part of the control unit that stores the instructions that needs to be

performed. The control unit accesses this register then decides what to do next. After the

control unit gets instructions from the IR, it starts the decoding processes. In this step, the

control unit decides what the instructions mean and directs the necessary data to be moved

from other memory to the arithmetic logic unit. The instruction decoder is used here and can

analysis the instruction data and figure out what to do to complete the job. It can also tell the

program’s counter to increment or reset to zero, and tell the arithmetic logic unit what

operation to perform. After the instruction decoder analyzes the data, the control unit sends

them to the arithmetic logic unit to execute, and this is the third step. The ALU will calculate

the result as how the control unit wants it, then the control unit sends the result back to the

memory as the last step. This is how a CPU works alone. It also needs other computer parts

to help to finish the processes. Like RAM, system bus, and clock. (Wikipedia)

The RAM which stands for random access memory, it is a type of storage in a computer.

It can store program and data currently used. The user can use a mouse or keyboard, etc. to

send instructions to the computer. The computer saves those instructions in a form of binary

code in the RAM. The binary code is a type of machine language which is using combination

of 0s and 1s. The instruction register which is in the control unit can get this data from the

RAM through the system bus. The system bus or front side bus (FSB) is like an expressway

between the CPU, RAM and other devices in the system. When the instruction register get

the instructions from the RAM, the CPU start to work. The CPU goes though the fetch,

decode, and execute steps repeatedly which forms a fetch-decode-execute cycle, and this

cycle regulate by the clock rate. The clock rate is an electronic clock in computer that delivers

a steady pulse to the CPU. The speed of CPU can process instructions depend on the clock

rate, increasing the clock rate will decrease the time required to complete each particular

instruction. (Brain)

The CPU is the brain of a computer, and that is why I want to research more on it after I

have completed my research paper. I talked about the history of CPU in my research paper.

The first CPU for EDVAC fills up a whole room. Now CPU has a size roughly as a large

postage stamp. In the future, as new technologies come out, the CPU will smaller and more

powerful. The evolution of the CPU could bring the evolution of the computer. So, the CPU

is the brain and it’s the most important part in the computer.

Works Citied

Central processing unit (2007, March 9). Retrieved March 11, 2007, from

http://en.wikipedia.org/wiki/Central_processing_unit

Brain, M. (2000, April). How Microprocessors Work. Retrieved March 13, 2007, from

http://computer.howstuffworks.com/microprocessor.htm