Page 143 - DCAP403_Operating System

Operating System

Notes low priority process. After this we should page out all of its remaining pages and freeing all of
its allocated frames. This provision introduces a swap in, swap-out level of intermediate CPU
scheduling. Let take a example of a process that does not have enough number of frames. If
the process does not have the number of frames it needs to support pages in active use, it will
quickly page fault. The only option remains here for process is to replace some active pages with
the page that requires a frame. However, since all of its pages are in active use, it must replace a
page that will be needed again right away. Consequently, it quickly faults again and again that
mean replacing pages that it must bring back in immediately. This high paging activity is called
Thrashing. Or we can say that a process is Thrashing if it is spending more time in paging then
executing. Thrashing results in severe performance problems.

7.13 Summary

The part of the operating system that manages the memory hierarchy is the memory
manager.
It keeps track of parts of memory that are in use and those that are not in use, to allocate
memory to processes when they need it and de-allocate it when they are done, and to
manage swapping between main memory and disk when main memory is too small to
hold all the processes.
Memory is the electronic holding place for instructions and data that the computer’s
microprocessor can reach quickly.

The memory manager is a part of operating system which is responsible for allocating
primary memory to processes and for assisting the programmer in loading and storing the
contents of the primary memory.
Overlaying means replacement of a block of stored instructions or data with another.
Overlay Manager is part of the operating system, which loads the required overlay from
external memory into its destination region in order to be used.
An address generated by the CPU is commonly referred to as a logical address and an
address seen by the memory unit – that is, the one loaded into the memory-address register
of the memory – is commonly referred to as a physical address.
Memory Management Unit (MMU) is a computer hardware component responsible for
handling accesses to memory requested by the CPU. It is also known as Paged Memory
Management Unit (PMMU).

7.14 Keywords

Logical Address: An address generated by the CPU is commonly referred to as a logical
address.
Memory Management Unit (MMU): It is a computer hardware component responsible for
handling accesses to memory requested by the CPU.

Memory Manager: The memory manager is a part of operating system which is responsible for
allocating primary memory to processes and for assisting the programmer in loading and storing
the contents of the primary memory.
Memory: It is the electronic holding place for instructions and data that the computer’s
microprocessor can reach quickly.
Overlay Manager: It is part of the operating system, which loads the required overlay from
external memory into its destination region in order to be used.

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