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Unformatted text preview: less than n. This is because when multiple processors cooperate to execute the
programs or subprograms, a certain amount of overhead is incurred in keeping
everything working correctly.
This overhead, plus contention for shared
resources, lowers the expected gains from additional processors.
2. Better Reliability. Due to multiplicity of processors, multiprocessor systems
also have better reliability than single-processor systems. In a properly designed
multiprocessor system, if one of the processors breaks down, the other
processor(s) automatically takes over the system workload until repairs are made.
Thus a complete breakdown of such systems can be avoided. For example, if a
system has 4 processors and one fails, then the remaining 3 processors can be
utilized to process the jobs submitted to the system. Thus, the entire system runs
only 25% slower, rather than failing altogether. This ability of a system to
continue providing service proportional to the level of non-failed hardware is
called graceful degradation feature.
Multiprocessing systems, however, require a very sophisticated operating system
to schedule, balance, and coordinate the input, output, and processing activities of
multiple processors. The design of such an operating system is a complex and time
taking job. Moreover, multiprocessing systems are expensive to procure and
maintain. In addition to the high charge paid initially, the regular operation and
maintenance of these systems is also a costly affair.
Time-sharing is a mechanism to provide simultaneous interactive use of a
computer system by many users in such a way that each user is given the
impression that he/she has his/her own computer. It uses multiprogramming with a
special CPU scheduling algorithm to achieve this.
A time-sharing system has many (even hundreds of) user terminals simultaneously
connected to the same computer. Using these terminals, multiple users can simultaneously work on the system. The multiprogramming feature allows
multiple user programs to simultaneously reside in the main memory. The special
CPU scheduling algorithm us...
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This document was uploaded on 04/07/2014.
- Spring '14