A special file used by the windows operating system to hold data which does not fit or is not currently required in the PC's memory . If you are running more than one application program on your PC you normally will be using one while the other is in the background waiting for your next instruction. Windows will make sure that the program you are running gets the memory it requires and it will move any memory space the other program has allocated to the swapfile. When you want to use the second program it will swap the information back from the swapfile into memory and move the other programs information to the swapfile. Windows creates the swapfile on the harddisk of the PC when you login.