Programs can access memory locations > address space addresses.
For example, a 16-bit program can be loaded and executed in memory addresses larger than 64K. Remember, even with virtual memory, a program cannot be larger than the CPUs address space.
Relocation
Programs can be loaded anywhere in memory without the need to relocate the code; virtual memory will perform the address translation at run-time.
Paging
Operating systems can divide programs into pieces and manage those pieces with simple allocation algorithms.
Protection
Virtual memory makes it impossible for one program to access the memory locations of another program. Access bits in the page table (typically, X R W) also can protect a program from itself.
Code sharing
Multiple processes can use the same code. For example, many users can share one copy of the C compiler.
Data sharing
Multiple programs can share the same data; unix pipes are a good example of data sharing between programs.
Only part of a program need be in memory (demand paging)
The operating system can load pages as they are needed. Don't confuse this feature with swapping; swapping means the entire program is moved to disk.
Using demand paging, a program can access addresss space > physical memory
You can write programs larger than memory; this is a great marketing ploy but, in practice, is not particularly important.

Last updated on 8/18/99