A swap partition (at least 256 MB) — swap partitions are used to support virtual memory. In other words, data is written to a swap partition when there is not enough RAM to store the data your system is processing.
If you are unsure about what size swap partition to create, make it twice the amount of RAM on your machine. It must be of type swap.
Creation of the proper amount of swap space varies depending on a number of factors including the following (in descending order of importance):
Swap should equal 2x physical RAM for up to 2 GB of physical RAM, and then an additional 1x physical RAM for any amount above 2 GB, but never less than 32 MB.
M = Amount of RAM in GB, and S = Amount of swap in GB, then
If M < 2
S = M *2
S = M + 2
Using this formula, a system with 2 GB of physical RAM would have 4 GB of swap, while one with 3 GB of physical RAM would have 5 GB of swap. Creating a large swap space partition can be especially helpful if you plan to upgrade your RAM at a later time.
For systems with really large amounts of RAM (more than 32 GB) you can likely get away with a smaller swap partition (around 1x, or less, of physical RAM).