A computer is a machine for manipulating
data according to a list of instructions known as a program.
Computers are extremely 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. Therefore, computers with capabilities
ranging from those of a personal digital assistant to a supercomputer
may all perform the same tasks, as long as time and memory capacity
are not considerations. Therefore, the same computer designs may be
adapted for tasks ranging from processing company payrolls to controlling
unmanned spaceflights. Due to technological advancement, modern electronic
computers are exponentially more capable than those of preceding generations
(a phenomenon partially described by Moore's Law).
Computers take numerous physical forms. Early electronic computers were
the size of a large room, while entire modern embedded computers may
be smaller than a deck of playing cards. Even today, enormous computing
facilities still exist for specialized scientific computation and for
the transaction processing requirements of large organizations. Smaller
computers designed for individual use are called personal computers.
Along with its portable equivalent, the laptop computer, the personal
computer is the ubiquitous information processing and communication
tool, and is usually what is meant by "a computer". However,
the most common form of computer in use today is the embedded computer.
Embedded computers are usually relatively simple and physically small
computers used to control another device. They may control machines
from fighter aircraft to industrial robots to digital cameras.
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