A computer is a device capable of processing data according to a program — a list of instructions. The data to be processed may represent many types of information including numbers, text, pictures, or sound.
Computers can be enormously versatile. In fact, they are universal information processing machines. According to the Church-Turing thesis, a computer with a certain minimum threshold capability is in principle capable of performing the tasks of any other computer, from those of a personal digital assistant to a supercomputer. Therefore, the same computer designs have been adapted for tasks from processing company payrolls to controlling industrial robots. Modern electronic computers also have enormous speed and ability for information processing compared to earlier designs, and they have become exponentially more powerful over the years (a phenomenon known as Moore's Law).
Computers are available in many physical forms. The original computers were the size of a large room, and such enormous computing services still exist for specialized scientific computation - supercomputers - and for the transaction processing requirements of large companies, usually called mainframes. Smaller computers for individual use, called personal computers, and their portable equivalent, the notebook computer, are ubiquitous information-processing and communication tools and be perhaps what most non-experts think of as "a computer". However, the most common form of computer in use today is the embedded computer, small computers used to control another device. Embedded computers control machines from fighter planes to digital cameras.