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Unformatted text preview: ts execution. Notice that this requires preserving
of the job's complete status information when the CPU is taken away from it and
restoring this information back before the CPU is given back to it again. To enable
this, the operating system maintains a process control block (PCB) for each loaded
process. A typical process control block is shown in Figure 14.6. With this
arrangement, before taking away the CPU from a running process, its status is
preserved in its PCB, and before the process resumes execution when the CPU is
given back to it at a later time, its status is restored back from its PCB. Thus the
process can continue execution without any problem.
values of various CPU
accounting and scheduling information
I/O status information
4. Proper job mix. A proper mix of I/O-bound and CPU-bound jobs is required
to effectively overlap the operations of the CPU and I/O devices. If all the loaded
jobs need I/O at the same time, the CPU will again be idle. Hence the main
memory should contain some CPU-bound and some I/O-bound jobs so that at least
one job is always ready to utilize the CPU.
5. CPU scheduling. In a multiprogramming system, often there will be situations
in which two or more jobs will be in the ready state waiting for CPU to be
allocated for execution. When more than one process is in the ready state when
the CPU becomes free, the operating system must decide which of the ready jobs
should be allocated the CPU for execution. The part of the operating system
concerned with this decision is called the CPU scheduler, and the algorithm it uses
is called the CPU scheduling algorithm.
Multitasking Technically speaking, multitasking, is the same as multiprogramming. That is,
multitasking is the system's capability to concurrently work on more than one task
(job or process). This means that whenever a task (job or process) needs to
perform I/O operations, the CPU can be used for executing some other task (job or
process) that is also residing in the system and is ready to use the CPU...
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This document was uploaded on 04/07/2014.
- Spring '14