The important components of a computer are the CPU, memory, graphics adapter, storage system and power supply. The motherboard connects these components together inside the case. Outside the case, the input system includes a keyboard and mouse, and the output display is usually a monitor.
Computers may also have expansion cards, such as sound cards or network adapters. In many cases, however, this functionality is included in the motherboard's chipset, and separate cards are not necessary.
Storage takes many forms in a computer. Typically, computers use at least one magnetic hard drive, and an optical drive for reading CDs and DVDs is a popular addition. Flash memory-based solid-state hard drives offer significant performance gains, but can be expensive.