Virtual Memory Facts
Terms in this set (4)
Simulated memory that is written to a page file on the hard drive. Virtual memory is used by OS to simulate physical RAM by using hard disk space
swapping or paging
The process of moving data from RAM to disk (and back).
Virtual Memory Manager (VMM)
In charge of swapping data between physical memory and the hard disk The VMM follows the following steps to manage applications:
1. The VMM assigns virtual addressing to an application. This is known as logical segmentation.
2. The application is then loaded into physical RAM (absolute address space). The process doesn't recognize its location in physical RAM; it only recognizes its virtual space.
3. As the user launches other applications, the VMM will allocate space to those applications in true physical RAM.
4. When there is no more space in physical RAM, the VMM will take the application that hasn't been used for the longest period of time and place it in the page file on the hard drive. This is known as paging out. Likewise, if an application is moved from the page file back into physical RAM, this is known as paging in.
5. If the system needs access to an application that has been paged out from physical RAM, this causes a problem known as a page fault. When this happens, the VMM will page out the program in the physical RAM that hasn't been used for the longest period of time to the page file on the hard drive, and will page in the application currently being accessed back to the physical RAM.
Virtual memory facts
Symptoms of low physical memory include slow system performance when running applications, or slow response when switching between applications
Disk thrashing occurs when the amount of physical memory is so low that data must constantly be moved from physical RAM, to disk, and back again.
To prevent disk thrashing, either run fewer applications or add more physical RAM
Accessing data stored in RAM is faster than accessing data on disk (or in virtual memory).
System's with a large amount of RAM do not require a large page file.
For a slight increase in performance, you can move the swap file to a different physical disk than is being used by the OS
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