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In loosely-coupled multiprocessor systems, each processor has its own local memory, input/output (I/O) channels, and operating system. Processors exchange data over a high-speed communication network by sending messages via a technique known as "message passing". Loosely-coupled multiprocessor systems are also known as distributed-memory ...
In multiprogramming systems, a task runs until it must wait for an external event or until the operating system's scheduler forcibly swaps the running task out of the CPU. Real-time systems such as those designed to control industrial robots, require timely processing; a single processor might be shared between calculations of machine movement ...
A multiprogramming or multitasking OS is a system that can execute many processes concurrently. Multiprogramming requires that the processor be allocated to each process for a period of time and de-allocated or issued at an appropriate moment.
Other authors prefer to refer to the operating system techniques as multiprogramming and reserve the term multiprocessing for the hardware aspect of having more than one processor. [2] [8] The remainder of this article discusses multiprocessing only in this hardware sense. In Flynn's taxonomy, multiprocessors as defined above are MIMD machines.
Conceptually, it is similar to cooperative multi-tasking used in real-time operating systems, in which tasks voluntarily give up execution time when they need to wait upon some type of event. This type of multithreading is known as block, cooperative or coarse-grained multithreading.
A multitasking operating system may just switch between processes to give the appearance of many processes executing simultaneously (that is, in parallel), though in fact only one process can be executing at any one time on a single CPU (unless the CPU has multiple cores, then multithreading or other similar technologies can be used). [a]
At the operating system level: Computer multitasking, including both cooperative multitasking and preemptive multitasking. Time-sharing, which replaced sequential batch processing of jobs with concurrent use of a system; Process; Thread; At the network level, networked systems are generally concurrent by their nature, as they consist of ...
The OS/360 also was the first popular operating system to support multiprogramming, such that the CPU could be put to use on one job while another was waiting on input/output (I/O). Holding multiple jobs in memory necessitated memory partitioning and safeguards against one job accessing the memory allocated to a different one.