Virtual Memory and Swap Space

[Ong Chin Soon]

What's the difference between virtual memory and swap space ?

[U.SivaKumar_2 · Accepted solution]

Hi,
They are same. Virtual memory is not possible without swap space.

regards,
U.SivaKumar

[T G Manikandan]

Whenever processes lag memory in the Real memory,processes which are idle are swapped or paged to the hard disk.
Later they are taken back to memory on need.

This area of memory which is used on the disk is the virtual memory which is also called as swap space.


Thanks

[Animesh Chakraborty]

A good document is here
http://www.usg.edu/OIIT/support/os/HP-UX_10.20/white_memman.html

[Wodisch]

Hi,

they are not quite the same: take an Xclient like "dtterm" for example.
It uses some megabytes of virtual memory, but only a small part of it on real RAM, and maybe nothing really on swapspace! Most of its program code may never be used at all and is therefor never paged into RAM. It does account for virtual memory, though. And some of the pages used in RAM may not be needed any more and hence become "freed" from RAM without problem.
If you use the command "size" on a codefile, it will tell you the amount of virtual memory needed on its start, but as the programs data can grow, so will its virtual memory.
If the reason for your question is to learn about the size of your swap space, then the answer is quite simple:
Set the kernel parameter "swapmemon" to 1, then you'll only need swap space for 1/4 of your RAM!
I.e. 1GB of RAM, and 256MB of swap space would be fine.

HTH,
Wodisch