Unformatted text preview: orm numerical calculations, with
little I/O operations. They are so called because they heavily utilize the CPU
during the course of their processing. Programs used for scientific and engineering
computations usually fall in this category of jobs.
2. I/O-bound jobs. These jobs normally input vast amount of data, perform very
little computation, and output large amount of information. They are so called
because during the course of their processing, their CPU utilization is very low
and most of the time they perform I/O operations. Programs used for commercial
data processing applications usually fall in this category of jobs.
In a uniprogramming system, the CPU will be idle whenever the job that is
currently being processed by the system performs I/O operations. With CPUbound jobs, the CPU idle time may not be significant, but for I/O-bound jobs the
CPU may be idle 80 to 90% of the time. Moreover, since I/O devices are slower
than the CPU by 20 to 100 times, the CPU idle time is significant even for CPUbound jobs that perform little I/O. The concept of multiprogramming was
introduced to minimize the idle time of the CPU by organizing multiple jobs in the
system so that the CPU always has something to execute. How this is done is
Multiprogramming is the name given to the interleaved execution of two or more
different and independent programs by the same computer. In Figure 14.3 we have
been introduced to the notion of having two programs in the main memory at the
same time - the operating system for overall system control and the user program
for performing user's job. In multiprogramming, this concept is carried one step
further by placing two or more user programs in the main memory and executing
them concurrently. With multiple user programs simultaneously residing in the
main memory, when a user program that was executing (using the CPU) starts
performing I/O operations, the CPU is allocated to another user program in the
main memory that is ready to use the CPU instead of allowing the CPU to be i...
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This document was uploaded on 04/07/2014.
- Spring '14