Designing a computer system consists of selecting the features that best match the processing jobs to be done. As each of these factors increases, the computer becomes able to handle more complex and larger tasks more rapidly. How the components of a computer are connected is called the computer's architecture and can affect the way the computer operates. The computer brain, called the CPU, controls operations, does arithmetic, keeps time, and regulates other computer components. Both serial and parallel interfaces allow computer components to communicate with each other.
Most computers have one CPU and process a single stream of data with a single instruction stream.
A single CPU can be multiprogrammed. Multiprogramming means that the processor alternates between tasks. ROM is commonly used to permanently store elementary software. Elementary software is often called firmware. RAM is temporary storage which can be erased and reused.