What is the Page-Fle (Swap-File) and how does it work?
The Page-file (or Swap-File as it's sometimes known) is 'Virtual Memory' that Windows uses on your Hard-Drive to store information you are using when you run out of memory.
If your system has a low amount of memory...e.g. 1Gb then when it can no longer use anymore free memory in the RAM then it starts writing (or reading) information to/from the page-file.
The Page-File is normally managed by the system but can be set by users themselves, some people disable it completely if they have large amounts of RAM installed such as 8Gb+ to save space on their hard-drives, this is ill-advised and can cause the system to crash.
On low memory systems this is how the computer 'slows down' because its spending most of its time swapping files to/from the disk, thats why IT Technicians will advise a memory upgrade on a system thats slow due to a low amount of RAM, on todays machines (as of 2015) 2Gb shoud be enough for basic use, but most computers nowadays come with at least 4Gb installed and thats enough to do quite a lot on, myself I personally have 8Gb installed.
As time goes on and new computers are released with higher spec, software manufacturers makes use of this extra space in the memory, and therefore if you try to run todays software on really old machines you will find that it will slow down quite a bit, an example - web browsers today typically use 'up-to' 1Gb of RAM if you have a few extensions installed and a few Tabs open, Chrome is a huge memory hog, I've had that using well over 1Gb before when i had many Tabs open (multipe pages open in the same browser).
So it's imprtant to ignore anydive on changing your page file, it should be left on "system managed" at all times, sometimes systems might not be configured like this so to find out do the following:
1. Hold down the Windows key left of the spacebar and tap 'R', this will open the run command.
2. Type in SystemPropertiesAdvanced then press enter.
3. Under performance click 'Settings'.
4. In the next window click 'Advanced' then click 'Change' under "Virtual Memory"
5. At the very top is the option "system managed", make sure it is clicked then press OK on all the open windows.
6. Reboot the computer.
Now Windows will expand the pagefile as much as needs be and make sure your system doesnt crash due to not having enough.