Computers and computer-like devices use virtual memory to expand the available system memory by borrowing data space from a mass storage device. Computers widely use virtual memory to work around space limitations in the system's main memory, or RAM. Other devices -- like tablets, smartphones and video game consoles -- also can use virtual memory; however, support varies depending on the software and the device.
Virtual Memory and Computers
Unless the feature has been disabled, all desktop and laptop computers running a mainstream operating system use virtual memory -- Windows, Mac OS X and Linux all use virtual memory. Virtual memory is important for multi-tasking operating systems because the computer doesn't have a fixed memory requirement: virtual memory comes into play when the computer is running more programs than it can store in the main system RAM. Additionally, computers may use virtual memory to help run programs that require more memory than the system actually has. Virtual memory allows computers to store inactive programs -- and inactive parts of programs -- and readily call them back into the main memory when needed.
Tablets, smartphones and personal media players use virtual memory to save the state of inactive, open apps to free the main system memory for use by other apps and the operating system. For example, Apple's iOS-running devices -- including iPads, iPhones and iPods -- all cache data to the mass storage memory. Additionally, some video game consoles -- including the PlayStation 4 -- use virtual memory to improve system performance. Game consoles may use virtual memory to pre-load content from the optical drive to reference it faster or to store game-related information that isn't being immediately used.
Virtual Memory Assists Main Memory
Virtual memory is a cost-effective alternative to adding more system RAM to a computer or computer-like device to meet memory needs. RAM is expensive, whereas mechanical and flash hard drives can provide substantial storage space for a much lower cost. Virtual memory is accessed through a pre-allocated "page-file" space on a storage device that's used to simulate RAM. However, virtual memory takes a performance hit over RAM, as even the fastest hard drives are still much slower than RAM. Virtual memory assists system RAM, but doesn't replace it. Adding more RAM will improve system performance better than adding more virtual memory.
Disk Thrashing Pitfalls
Improperly managed or overloaded virtual memory can cause the computer's performance to drop to a crawl: if the problem is bad enough, the computer will start "disk thrashing," a state when the computer's RAM and hard drive are constantly swapping information back and forth. Disk thrashing causes major system performance problems, and can eventually break the storage device if it goes on for too long.
- Microsoft Windows: What Is Virtual Memory?
- Apple iOS Developer Library: About the Virtual Memory System
- Redhat: Understanding the Virtual Memory
- Gamespot: Sony Confirms PlayStation 4 Developers can Use Flexible Memory
- University of Maryland Computer Science Department: Virtual Memory
- Crucial: Virtual Memory and Your Hard Disk Drive
- Computer Hope Jargon: Thrashing
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