A program in a computer instructs the Intel 386 or the CPU to address upto 4GB of memory using its 32 bits. Generally this memory is much more than that of the RAM of the machine. So the hardware provides the additional memory space for programmes to operate in this full 4GB space as virtual memory. The processor then translates the virtual addresses from an instruction to the correct physical equivalents. The process is called mapping. When the amount of free memory falls below the threshold , the virtual memory manager uses a tactic called automatic working- set trimming to restore the value above the threshold.
Windows XP implements virtual memory using demand paging with clustering. Clustering handles page faults by bringing in not only the faulting page but also several pages following the faulting page. When a process is first created , it is assigned a working – set minimum and maximum. The working set minimum is the minimum number of pages the process is guaranteed to have in memory. If sufficient memory is available, a process may be assigned as many pages as its working-set maximum. For most applications , the value of working-set minimum is 50 pages and that of working-set maximum is 345 pages. By default the virtual memory is set at 1.5 times the size of the RAM of the computer, by the Windows. Low virtual memory means the running program has the requirement of more space.
The virtual memory is always in action and cannot be turned off.
At times certain problems are faced with the virtual memory. A system shows ‘out of memory’ messages at he time of loading a program. These things happen due to various reasons. Such as the maximum number of pages set is low as per the requirement of a program being loaded, or less amount to disk space available to expand the pages to their maximum numbers. If the page file is loaded in another drive other than filling a minimum space in drive C. The corrupt files or bad shut downs may also give out such types of messages.