Virtual Memory: Swap File or Page File on Disk
The term virtual memory is used to describe memory that is not what it appears to be. Hard disk drive space is manipulated to seem like RAM. The combination of virtual memory and actual installed physical memory, gives the appearance of more memory than is actually installed on the system. Virtual memory is the basis of multitasking in Windows 9x. Without virtual memory, it would be almost impossible to run most of the software in use today. Windows 3.X and 9x all implement virtual memory in files called swap files. Software creates virtual memory by swapping files between RAM and the hard disk drive. This memory management technique is how more total memory is effectively created for the system applications to use. Note that since the hard drive is slower than normal RAM, an overall reduction in speed is encountered with virtual memory operations. In fact, virtual memory is the slowest of any memory model.

It is hard to think of any operating system since Windows 3x (Windows 9x, Windows NT/2000/XP, UNIX or Linux) that does not use some form of virtual memory operations. On older operating systems, there was often a permanent swap file having an extension of PAR. Today, most operating systems tend to utilize temporary swap files with an SWP extension. A permanent swap file is always present and is a constant size. A temporary swap file is created when Windows starts, and has a variable size. Control of Windows 95 (also Windows 98 and ME) Virtual Memory operations is established through the Control Panel [System][Performance] tab. Clicking the Virtual Memory button produces the Virtual Memory options screen. The default and recommended setting is [Let Windows manage my virtual memory settings]. The Windows 95 swap file is called WIN386.SWP. It is dynamically assigned and size is variable. The Windows 2000 swap file (page file) is named pagefile.sys. This file is created when Windows 2000 is installed. Its default size is typically set at 1.5 times the amount of RAM installed in the system.

RAM Drive
Setting aside a portion of RAM to emulate a drive can create a RAM drive. For example, on a machine that has a hard drive partitioned into drives C and D, a RAM drive of 4 MB (4096 KB) can be created as E with the command:

DEVICE=C: \DOS\RAMDRIVE.SYS 4096

This command is entered in the CONFIG.SYS file. The RAM drive will become the next available letter and can be any size specified up to the amount of RAM installed on the computer. Because data stored on the RAM DRIVE exists only in RAM, it is cleared on each reboot. This is certainly not a good place for storing data files being updated.