What is Virtual Memory?
A. Virtual Memory makes up for the lack of RAM in computers by using space on the hard disk as memory, Virtual Memory. When the actual RAM fills up (actually its before the RAM fills) then virtual memory is created on the hard disk. When physical memory runs out, the Virtual Memory Manager chooses sections of memory that have not been recently used and are of low priority and writes them to the swap file. This process is hidden from applications, and applications views both virtual and actual memory as the same. Each application that runs under Windows NT is given its own virtual address space of 4GB (2GB for the application, 2GB for the operating system). The problem with Virtual Memory is that as it writes and reads to the hard disk, this is much slower than actual RAM. This is why if an NT system does not have enough memory it will run very slowly.
A program instruction on an Intel 386 or later CPU can address up to 4GB of memory, using its full 32 bits. This is normally far more than the RAM of the machine. (The 32nd exponent of 2 is exactly 4,294,967,296, or 4 GB. 32 binary digits allow the representation of 4,294,967,296 numbers — counting 0.) So the hardware provides for programs to operate in terms of as much as they wish of this full 4GB space as Virtual Memory, those parts of the program and data which are currently active being loaded into Physical Random Access Memory (RAM). The processor itself then translates (‘maps’) the virtual addresses from an instruction into the correct physical equivalents, doing this on the fly as the instruction is executed. The processor manages the mapping in terms of pages of 4 Kilobytes each – a size that has implications for managing virtual memory by the system.
If your computer lacks the random access memory (RAM) needed to run a program or operation, Windows uses virtual memory to compensate. Virtual memory combines your computer’s RAM with temporary space on your hard disk. When RAM runs low, virtual memory moves data from RAM to a space called a paging file. Moving data to and from the paging file frees up RAM to complete its work. The more RAM your computer has, the faster your programs will generally run. If a lack of RAM is slowing your computer, you might be tempted to increase virtual memory to compensate. However, your computer can read data from RAM much more quickly than from a hard disk, so adding RAM is a better solution.
Virtual memory is a common part of most operating systems on desktop computers . It has become so common because it provides a big benefit for users at a very low cost. Most computers today have something like 64 or 128 megabytes of RAM (random-access memory) available for use by the CPU (central processing unit). Often, that amount of RAM is not enough to run all of the programs that most users expect to run at once. For example, if you load the Windows operating system, an e-mail program, a Web browser and word processor into RAM simultaneously, 64 megabytes is not enough to hold it all. If there were no such thing as virtual memory , your computer would have to say, “Sorry, you cannot load any more applications. Please close an application to load a new one.” With virtual memory, the computer can look for areas of RAM that have not been used recently and copy them onto the hard disk . This frees up space in RAM to load the new application. Because it does this automatically, you don
