Multitasking and Multithreading

The most significant job an OS does is to manage memory efficiently and control how applications use system resources. An OS that does memory management and task scheduling permits both context switching and multitasking. Context switching suspends activity when one operation is pushed to the background and another is brought to the foreground; only the application in the foreground window remains active. Context switching is sufficient for many work environments and provides dramatic productivity gains over the exiting and loading of different applications in single-tasking environments.

Multitasking , on the other hand, runs multiple operations concurrently. It makes sense mainly in multiuser environments. Its benefits become really noticeable with long and comple x tasks, such as heavy database queries, program compilation, and complex graphics processing.

Even though all three OSes use preemptive multitasking for 32-bit applications, only OS/2 Warp and Windows NT Workstation use it for older, 16-bit applications. Windows 95 uses cooperative multitasking for 16-bit DOS and Windows applications.

For preemptive multitasking to operate effectively requires a task-scheduling scheme, where the scheduler selectively dispatches and suspends multiple concurrent tasks. Cooperative multitasking relies on applications to relinquish control of the processor so that other applications get a turn. This means the applications are in control, not the OS.

The multithreading capability of today's 32-bit OSes provides more power than simple multitasking does. The OS can execute multiple tasks simultaneously, and it can run multiple processes concurrently. The kernel breaks down tasks into singular processes and runs each process as a single thread. Interprocess communications (IPC) allows the different threads to talk with each other by passing data back and forth.

The real advantage of multithreading is that it makes it much easier to do multitasking. Multithreading allows programs to multitask within themselves. Applications that can benefit considerably from multithreading include background pagination and formatting, spell-checking, complex database searches, document control, and dual-channel communications.

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Tasks vs. Threads

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