Computer hardware, consisting mainly of the central processing unit (CPU), random access memory (RAM), and various peripheral devices, provides the physical components needed for computation, but hardware by itself can do nothing useful without the explicit step-by-step instructions provided by computer software.

Computer software consists of sequences of instructions for the CPU. A sequence of instructions for the CPU is typically referred to as a program. Programs vary in size and complexity and can be as simple as a utility that prints the current time and date on the screen or as large and complicated as a spreadsheet application or a full-featured word processor. Each instruction in a program directs the CPU to do one simple task, such as accessing the contents of a memory location, adding two numbers, or jumping to a different part of the program depending on the value contained in a register...