| Virtual Address Space |
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| CATEGORIES ABOUT VIRTUAL ADDRESS SPACE | |
| virtual memory | |
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OVERVIEW When you run an application on a 32-bit es (from 0 to 232-1) in that space can have a single Byte as value. Initially, none of them have values.Virtual Memory is easiest to comprehend if one thinks in terms of the VAS, and not the Physical Memory of the machine nor the size of its Page File . Byte values in the VAS come only from byte values in a File . The OS manages the mapping between the VAS and the files that hold its values. Physical memory comes in various flavors: On-chip Cache, Off-chip Cache , and System Memory . As far as the process is concerned, system memory is just another level of cache used by the OS. System memory has a lot to do with performance, but nothing to do with the architecture of a process. The process architecture is based on the VAS. Physical memory is used by the OS to map values from file bytes to VAS addresses: process memory is VAS memory, not physical memory. (''In the following description, the terminology used will be particular to the Windows NT OS, but the concepts are applicable to other virtual memory operating systems'') When a process starts it has a 4GB VAS with no values. The -'s in the VAS line have no values. Using or setting values in such a VAS would cause a Memory Exception . 0 4GB |
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