What Is Virtual Memory Management?

Regular Memory

• There are two types of physical computer memory: ROM and RAM. ROM is read-only memory and holds instructions needed to boot a computer. Random access memory (RAM) resides on computer chips placed on RAM sticks. Computer manufacturers then install the RAM sticks on computer motherboards. Windows and other software programs can write to RAM at any time. Unfortunately, a computer can only hold a limited amount of RAM.
  
  

Virtual Memory

• As different programs add data to RAM, eventually the RAM area fills up. Without virtual memory, other programs cannot store data in RAM. Windows solves this problem by examining the data in RAM. If Windows finds RAM data that no program has accessed in a while, it removes that data and stores it on the hard drive in an area called the pagefile. Other programs that need to use the RAM are then free to move their data there. Virtual memory describes the process of moving and managing data between physical RAM and the pagefile. Software developers do not need to worry about running out of memory because virtual memory will simulate the memory that their programs need to function.
  
  

History

• In 1958, the University of Manchester needed a way to simplify the process of moving computer memory between different areas of its computers. It invented virtual memory to work on one of the world's first supercomputers, the Ferranti Atlas. Computer scientists and engineers worked on new software techniques and hardware, perfecting the virtual memory process. Virtual memory finally made it to personal computers in 1985 when Intel introduced its 80386 line of microprocessors..
  
  

Interesting Facts

• According to Microsoft, Windows is always using virtual memory, even when enough physical RAM exists to handle all memory requests. The optimal size of a pagefile depends on the amount of physical RAM on the computer and the types of memory requests that programs need at a particular time. Microsoft recommends a normal pagefile size equal to one and one-half times the amount of RAM available on the computer. The area of RAM that Windows moves to the pagefile is a "page." The size of a page is 4 KB. Windows can spread out the pagefile across multiple partitions. However, only one pagefile exists per partition.
  
  

Pros and Cons

• Virtual memory enables you to run memory-intensive software on computers that do not have sufficient amounts of physical RAM. Use of virtual memory also increases CPU utilization because more programs become memory-resident. However, virtual memory is slower than regular memory because Windows must move it to the hard drive and retrieve it from there when programs need it.