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The Difference Between

What is the difference between time sharing and multiprogramming?

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2013-03-14 20:44:20

Both terms are used to describe a computer process known as

multi-tasking, where a single CPU core switches between tasks

periodically to reduce inefficiency and wasted time, and to allow

the user to perform multiple tasks at the same time. The difference

between the two are technical distinctions, rather than a

difference in their intended effect.


Multiprogramming was the first form of multi-tasking, and

introduced in the the concept of yielding. When an instruction

could not be completed immediately (such as when reading from a

disk or other slowperipheral, the current task was set aside, and

another task would run until the data from the paused task was

ready.


Some time later, time sharing was introduced to allow more

fine-grained control over the yielding process. The first form was

known as cooperative time sharing. In this model, a program would

run for a while and then willingly relinquish control so that

another process could have a chance. This was referred to as

cooperative time sharing. This model had some drawbacks, as

programs could be written incorrectly and fail to yield in a timely

manner, causing the system to become slow and unresponsive.

Additionally, programs cooperated in the same unprotected memory

space, so a crash of one program meant that the entire system could

be brought down by a single fault.


Advances in hardware allowed for the processes to be interrupted

by the operating system. This brought about the next generation of

time sharing, known as preemptive time sharing. Along with this

model came advances in virtual memory that allowed each program to

run in its own virtual memory space. No longer would a single

program cause a systemic crash, and a program could no longer fail

to yield (in theory, at least).


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