History
See also: History of operating systemsBy the early 1960s computer control software had evolved from Monitor control software, e.g., IBSYS, to Executive control software. Computers got "faster" and computer time was still neither "cheap" nor fully used. It made multiprogramming possible and necessary.
Multiprogramming means that several programs run "at the same time" (concurrently, including parallel and non-parallel). At first they ran on a single processor (i.e., uniprocessor) and shared scarce resources. Multiprogramming is also basic form of multiprocessing, a much broader term.
Programs consist of sequences of instructions for processors. A single processor can run only one instruction at a time: it is impossible to run more programs at the same time. A program might need some resource (input ...) which has a large delay, or a program might start some slow operation (output to printer ...). This would lead to processor being "idle" (unused). To use processor at all times, the execution of such a program is halted. At that point, a second (or nth) program is started or restarted. To the user, it will appear that the programs run at the same time (hence the term, concurrent).
Shortly thereafter, the notion of a 'program' was expanded to the notion of an 'executing program and its context'. The concept of a process was born.
This became necessary with the invention of re-entrant code.
Threads came somewhat later. However, with the advent of time-sharing; computer networks; multiple-CPU, shared memory computers; etc., the old "multiprogramming" gave way to true multitasking, multiprocessing and, later, multithreading.
Read more about this topic: Process (computing)
Famous quotes containing the word history:
“What has history to do with me? Mine is the first and only world! I want to report how I find the world. What others have told me about the world is a very small and incidental part of my experience. I have to judge the world, to measure things.”
—Ludwig Wittgenstein (1889–1951)
“We aspire to be something more than stupid and timid chattels, pretending to read history and our Bibles, but desecrating every house and every day we breathe in.”
—Henry David Thoreau (1817–1862)
“No one can understand Paris and its history who does not understand that its fierceness is the balance and justification of its frivolity. It is called a city of pleasure; but it may also very specially be called a city of pain. The crown of roses is also a crown of thorns. Its people are too prone to hurt others, but quite ready also to hurt themselves. They are martyrs for religion, they are martyrs for irreligion; they are even martyrs for immorality.”
—Gilbert Keith Chesterton (1874–1936)