Computers may seem like overly complicated pieces of machinery, with wires and screws and circuit boards crammed into every square inch of the computer case. The truth is that, although there are many accessories available, a computer only truly requires a few key, essential pieces to operate properly. Each piece offers many options in terms of speed, size and capacity, and your individual needs and intended use of the computer should dictate how fast or powerful a system you truly need. Computer Case And MotherboardThe first most obvious part mandatory for a computer is the case, also known as the tower. The computer case houses and protects all the delicate internal electrical components that allow the computer to function and perform complicated tasks. Within the case rests the motherboard, which acts as the nervous system of a computer. It connects all other components to each other, allowing them to work together to run programs, access memory and read the hard drive. Some motherboards will not physically fit into some computer cases, so verify the fit if building your own system. CPU And RAMThe CPU, or central processing unit, acts as the actual brain of the computer and is the part responsible for every computation and process the machine performs. Every action and program is controlled by the CPU, and the higher the megahertz number, listed as MHz, the faster the CPU performs processes. The RAM, or random access memory, is a kind of temporary holding file for data the CPU requires while running processes. The higher the number of megabytes, or MB, in the RAM chip, the more storage capacity it offers. Some motherboards come with a CPU and RAM pre-installed, while others require the separate purchase of all three components. The hard drive provides permanent storage of information and data. Personal documents, program files and your operating system all rest on the hard drive. Hard drives are available in sizes ranging from gigabytes, or GB, to terabytes, or TB. Programs and other software are typically installed via CDs, and require a CD/DVD drive to read these disks. Various options exist for these drives, as some only read disks while others can read and write them. Having all these intricate, powerful components inside your computer case do you no good if you can't interact with the data they contain. Input and output devices, or interface devices, allow interaction with the programs and data within the computer, and the three vital components are the monitor, keyboard and mouse. The computer monitor displays the various text, graphics and data held within your computer, while the keyboard and mouse allow you to manipulate and interact with that data. The video or graphics card allows the computer to communicate and display graphics on the monitor, while the sound card provides output for audio signals. In some cases, these two cards are included on the motherboard. For users serious about their visual and audio computer experience, such as gamers or those who create videos on their computers, higher quality sound and video cards are available separately. Power and CoolingTo power all these sophisticated components within your computer case, you'll need a power supply. Most cases come with a power supply pre-installed, and most power supplies also contain a built-in fan for added cooling. The components inside a computer case generate heat during operation, and this heat could cause damage if allowed to build up to an overly-high temperature. Internal fans help to dissipate this heat by venting it through the air vents cut into the case to protect your computer from overheating.