Software is a collection of instructions and data that tell a computer how to work. This is in contrast to hardware, from which the system is built and actually performs the work. In computer science and software development, software is all information processed by computer systems, including programs, libraries and related non-executable data such as online documentation or digital media. Software and hardware require each other and neither can be used on their own.
At the lowest programming level, executable code consists of machine language instructions supported by an individual processor—typically a central processing unit or a graphics processing unit. Machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user. An instruction may also invoke one of many input or output operations, for example displaying some text on a computer screen; causing state changes which should be visible to the user.