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 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 disc 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 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 in this particular example the motherboard is placed vertically which is quite common one side of the motherboard is accessible from the back of the computer case this includes the various connectors for input and output devices as well as expansion slots for additional peripherals the motherboard also contains the central processing unit CPU although it can be difficult to see a large fan is often placed on top of the CPU to avoid overheating the motherboard also contains the main memory of the computer the hard disk drive provides the mass storage for the computer system and is connected to the motherboard using a set of wires an optical drive can be accessed from the front of the computer case the power supply is located in the back of the computer case and often has its own fan for cooling every manufacturer will use a slightly different design but the general layout in this diagram is fairly typical computer system units come in different shapes and sizes referred to as form factors this is typically determined by the type of motherboard since this is the largest and most central component names for different sizes vary between manufacturers but are often referred to as full tower mini Tower slim case or small form factor tower models can typically only stand upright while some of the smaller models can also lie flat so you can save space by placing the monitor on top of the case a computer system unit is the enclosure that contains the main components of a computer typically made of steel or aluminum it holds all other components together and protects the sensitive electronic parts from the outside elements