Until recently, almost all consumer PCs used 32-bit processors. The total number of addresses available in the virtual memory – the total amount of data the computer can keep in its working area for applications – is determined by the width of the registers on the computer processor. When the user needs these processes, the page table remaps them into physical memory, where the user can access them at high speeds.
If the amount of memory demanded by all running processes exceeds the available physical memory (RAM), the paging table stores low-priority processes on the hard drive in the page file, which is much slower than RAM. A paging table is responsible for moving segments of virtual memory into physical memory as necessary. This solution is often referred to as “virtual memory,” in which the computer simulates having large amounts of contiguous physical memory. The solution for this is that programs store some of their data on the hard drive and copy it back and forth to physical memory as needed. This is especially true when multiple processes or applications execute simultaneously. Often the maximum size of the physical memory on a computer is less than the amount needed for all running programs.
To understand why 64-bit operating systems are a logical step in the evolution of the PC, consider this background information.
