The Mechanical APDL program requires memory in which to reside and memory to use as work space. The work space default is 2 GB (2048 MB) on Linux and Windows systems.

As shown in Figure 20.1: Comparing Available Memory, the total memory required for the program can exceed the amount of physical memory available. The additional memory comes from system virtual memory, which is simply a portion of a computer's hard disk drive used by the system to supplement physical memory.

The disk space used for system virtual memory is called swap space, and its associated hidden system file is called the swap file. (sometimes called a page file). Other systems maintain multiple files or even dedicated disk sectors for virtual memory. The amount of swap space required for the program depends mainly on the amount of physical memory available and the amount of work space allocated.

Because hard disk drives are much slower than system memory, and writing data from memory to disk (or reading data from disk to memory) incurs significant overhead, it is best to avoid virtual memory usage insofar as possible; otherwise, performance is severely degraded.

Figure 20.1: Comparing Available Memory

System virtual memory is used to satisfy additional memory requirements.