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| = Under Construction = | = Virtual Memory = There are two main motivations for Virtual Memory: 1. To allow efficient and safe sharing of memory among multiple programs 1. To remove the programming burdens of a small, limited amount of main memory. Virtual memory implements the translation of a program's address space to physical addresses. This translation process '''enforces protection''' of a program's address space from other programs. In times past programmers had to make sure their programs fit in the memory available, Virtual memory overcomes this by relieving the programmer of this task. '''KEY: A Virtual Memory Block is called a page KEY: A Virtual Memory Miss is called a page fault KEY: The CPU produces a Virtual Address.''' The process of mapping virtual memory addresses to physical memory address is called memory mapping or '''address translation'''. Virtual memory also provides '''relocation''' functionality. This allows us to load the program in any physical memory location (remember that DOS required you to run your program in the lower 640K of memory). Further memory is allocated in fixed size blocks ('''pages''') eliminating the need to find a contiguous block of memory to allocate to a program. (Remember that memory references in a program are offsets that assume contiguous memory use.) FORMAT: ||Virtual Page Number||||Page Offset|| Note that since physical memory is allocated in pages, that the page offset for virtual and physical addresses don't change. https://www.scotnpatti.com/images/vitualMemorytranslation.jpg |
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Virtual Memory
There are two main motivations for Virtual Memory:
- To allow efficient and safe sharing of memory among multiple programs
- To remove the programming burdens of a small, limited amount of main memory.
Virtual memory implements the translation of a program's address space to physical addresses. This translation process enforces protection of a program's address space from other programs.
In times past programmers had to make sure their programs fit in the memory available, Virtual memory overcomes this by relieving the programmer of this task.
KEY: A Virtual Memory Block is called a page KEY: A Virtual Memory Miss is called a page fault KEY: The CPU produces a Virtual Address.
The process of mapping virtual memory addresses to physical memory address is called memory mapping or address translation. Virtual memory also provides relocation functionality. This allows us to load the program in any physical memory location (remember that DOS required you to run your program in the lower 640K of memory). Further memory is allocated in fixed size blocks (pages) eliminating the need to find a contiguous block of memory to allocate to a program. (Remember that memory references in a program are offsets that assume contiguous memory use.)
FORMAT:
Virtual Page Number |
Page Offset |
|
Note that since physical memory is allocated in pages, that the page offset for virtual and physical addresses don't change.
https://www.scotnpatti.com/images/vitualMemorytranslation.jpg
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