19-01-2013, 03:42 PM
A PRESENTATION ON VIRTUAL MEMORY (PAGING)
MEMORY (PAGING).pptx (Size: 87.56 KB / Downloads: 35)
Introduction
The memory unit is an essential component in any digital computer since it is needed for storing programs and data.
The memory unit that communicate with the CPU directly is called MAIN MEMORY.
Devices that provide backup storage is called AUXILIARY MEMORY.
A special very-high-speed memory called CACHE MEMORY is used to increase the speed of processing.
Virtual Memory
Virtual memory is a concept used in large computer system that permit user to construct programs as though a large memory space were available, equal to the total auxiliary memory.
Each address that is referenced by the CPU goes through an address mapping from the so called virtual address to a physical address in main memory.
ITS AN ILLUSION.
Address space & Memory space
An address used by a programmer will be called a virtual address, and the set of such address is the address space.
An address in main memory is called a location or physical address. The set of such location is called the memory space.
Address mapping using PAGES
The physical memory is broken sown into groups of equal size called blocks, which may range from 64 to 4096 words each. The term page refers to groups of address space of thr same size.
A page and a block are splt into groups of 1 K words, a page refers to the organization of address space, while a block refers to the organization of memory space.
Associative Memory page Table
A more efficient way to organize the page table would be to construct it with a number of words equal to the number of blocks in main memory. In this way the size of the memory is reduced and each location is fully utilized .
We replace the random access memory page table with an associative memory of four words.
Page replacement
A virtual memory system is a combination of hardware and software techniques. The memory management software system handles all the software operations for the efficient utilization of memory space. It must decide
Which page in main memory ought to be removed to make room for a new Page
When a new page is to be transferred fro auxiliary memory to main memory, and
When the page is to placed in main memory.