What is a Computer System Unit? - Function, Components & Definition

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  • 0:01 Definition
  • 0:37 Functions
  • 1:39 Inside the Computer Case
  • 2:49 Form Factor
  • 3:26 Lesson Summary
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Lesson Transcript
Paul Zandbergen

Paul has a PhD from the University of British Columbia and has taught Geographic Information Systems, statistics and computer programming for 15 years.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

A computer system unit is the enclosure that contains the main components of a computer. It is also referred to as a computer case or tower. Read on to learn about the functions and components that go into a computer system unit.


A typical desktop computer consists of a computer system unit, a keyboard, a mouse, and a monitor. The computer system unit is the enclosure for all the other main interior components of a computer. It is also called the computer case, computer chassis, or computer tower. Cases are typically made of steel or aluminum, but plastic can also be used. While most computer cases are rather dull, black, metal boxes, some manufacturers try to give the unit some flair with color and special design elements.

Computer system unit
computer case blue


The primary function of the computer system unit is to hold all the other components together and protect the sensitive electronic parts from the outside elements. A typical computer case is also large enough to allow for upgrades, such as adding a second hard drive or a higher-quality video card. It is relatively easy to open up a computer system unit to replace parts and install upgrades. In contrast, it is quite difficult to open up a laptop computer, which is not designed with replacements and upgrades in mind.

In most computer system units, the front side contains the elements a user needs frequently, such as the power button, an optical disk drive, an audio outlet for a pair of headphones, and a number of USB connections. The back side contains all other connections - for power, monitor, keyboard, mouse, Internet connection, and any other peripheral devices. There are typically more connections than the minimum necessary to allow for expansion.

Front (left) and back (right) of a computer system unit
desktop front and back

Inside the Computer Case

Once you open up a computer case, it can initially be difficult to recognize the various components, especially all the different wires. However, if you look closely, you will probably start to recognize a number of components.

Major components inside a computer case
computer case components labelled

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Additional Activities

Modified True or False Exercise


Check your knowledge of the lesson on the function and definition of a computer system unit by determining whether the following statements are true or false. For this activity, print or copy this page on a piece of paper. Write TRUE if the statement is valid and FALSE if otherwise on the blank space provided. If the statement is FALSE, write down the word or phrase that makes it wrong.

_____ 1. The central processing unit houses all the internal components of the computer and protects these sensitive components from elements that may cause harm.

_____ 2. The motherboard holds together the central processing unit or CPU and connectors for input and output devices in a computer.

_____ 3. Computer components are vulnerable to damage from dust and spilled liquid.

_____ 4. A USB keyboard is part of the computer system unit.

_____ 5. A hard disk functions as a storage media for the computer system.

_____ 6. A large fan is used to draw cooler air into the computer case to avoid overheating of components, such as the CPU.

_____ 7. The main memory of the computer, also referred to as RAM, is attached to the power supply.

_____ 8. The form factor is the size, configuration, or physical arrangement of a computer system unit.

Answer Key

1. FALSE, central processing



4. FALSE, UBS keyboard



7. FALSE, power supply


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