The central processing unit (CPU) carries out the computer's instructions and communicates with other components. A heat sink cools the CPU using thermal compound. There are two main processor manufacturers, AMD and Intel, which make dual and quad-core processors. Memory includes RAM, ROM, and cache memory. Storage devices include hard disk drives, solid state drives, external hard drives, and SCSI devices. Other components are adapter cards, sound/video cards, the motherboard, and the power supply.