In computing, multitasking is a method by which multiple tasks, also known as processes In computing, a process is an instance of a computer program, consisting of one or more threads, that is being sequentially executed by a computer system that has the ability to run several computer programs concurrently, share common processing resources such as a CPU The Central Processing Unit or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task. Multitasking solves the problem by scheduling Scheduling is a key concept in computer multitasking, multiprocessing operating system and real-time operating system designs. Scheduling refers to the way processes are assigned to run on the available CPUs, since there are typically many more processes running than there are available CPUs. This assignment is carried out by software known as a which task may be the one running at any given time, and when another waiting task gets a turn. The act of reassigning a CPU from one task to another one is called a context switch A context switch is the computing process of storing and restoring the state of a CPU such that multiple processes can share a single CPU resource. The context switch is an essential feature of a multitasking operating system. Context switches are usually computationally intensive and much of the design of operating systems is to optimize the use. When context switches occur frequently enough the illusion of parallelism Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level, instruction level, data, and task parallelism is achieved. Even on computers with more than one CPU (called multiprocessor Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them. There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly machines), multitasking allows many more tasks to be run than there are CPUs.
Operating systems may adopt one of many different scheduling strategies Scheduling is a key concept in computer multitasking, multiprocessing operating system and real-time operating system designs. Scheduling refers to the way processes are assigned to run on the available CPUs, since there are typically many more processes running than there are available CPUs. This assignment is carried out by software known as a, which generally fall into the following categories:
- In multiprogramming systems, the running task keeps running until it performs an operation that requires waiting for an external event (e.g. reading from a tape) or until the computer's scheduler forcibly swaps the running task out of the CPU. Multiprogramming systems are designed to maximize CPU usage.
- In time-sharing Time-sharing is sharing a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing. By allowing a large number of users to interact concurrently with a single systems, the running task is required to relinquish the CPU, either voluntarily or by an external event such as a hardware interrupt In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution. Time sharing systems are designed to allow several programs to execute apparently simultaneously. The expression 'time sharing' was usually used to designate computers shared by interactive users at terminals, such as IBM's TSO In computing, the Time Sharing Option is an interactive time-sharing environment for the lineage of IBM mainframe operating systems running from OS/MVT through MVS and OS/390 to the current z/OS. It fills the same purpose as the login sessions used by users on Unix. "Time-sharing" means that many persons can access MVS concurrently but, and VM/CMS CP/CMS was a time-sharing operating system of the late 60s and early 70s, known for its excellent performance and advanced features. It had three distinct versions:
- In real-time In computer science, real-time computing , or "reactive computing", is the study of hardware and software systems that are subject to a "real-time constraint"—i.e., operational deadlines from event to system response. By contrast, a non-real-time system is one for which there is no deadline, even if fast response or high systems, some waiting tasks are guaranteed to be given the CPU when an external event occurs. Real time systems are designed to control mechanical devices such as industrial robots, which require timely processing.
The term time-sharing is no longer commonly used, having been replaced by simply multitasking, and by the advent of personal computers and workstations rather than shared interactive systems.
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Dan Ackerman
Wed, 27 Jan 2010 19:41:00 GM
Ditto for the apparent lack of . multitasking. . Steve Jobs actually thinks the iPad is an entirely new category, somewhere between a handheld phone-size device and a full laptop. What do you think? Is the iPad a "real" . computer. , ...
