Since lots of people are taking an interest in this topic, I might provide an explanation on the relationship between the amount of RAM and the computer's perceived speed.
There are (roughly) two purposes of RAM in a modern operating system:
1. Storing the instructions and data of loaded applications
2. Storing copies of files that have been recently accessed (a cache), ie a duplicate of what's on the hard drive.
If a computer doesn't have enough RAM for purpose 1, it will use the hard drive to store the extra data and swap data between the RAM and hard drive based on when it's being accessed. This will typically result in the computer running very slugglishly (10 times slower) when a new application is loaded or when switching between applications, as data is swapped between the disk and RAM (causing a large and often audible amount of hard drive activity). Once this has occured, the computer will run smoothly again. In some cases, it may permanently be exceedingly slow if there's never a point at which it can operate without swapping data between the RAM and hard drive. Increasing the amount of available RAM will stop the computer running slugglishly under these circumstances.
If a computer has more than enough RAM for purpose 1, but not for purposes 1 and 2, it may occasionally run slugglishly, but not often. This will be in circumstances when the data used for purpose 1 has been copied to the hard drive to free memory for purpose two*. Increasing the amount of available RAM will result in a relatively small speed boost, as it will prevent these circumstances and allow for more hard drive data to be cached.
If the computer has enough RAM for both purposes, adding additional RAM will have
no speed benefit. If your computer is slow loading applications and opening files but otherwise instant, get a fast hard drive such as an SSD. Otherwise, time for a new machine.
As an example, my curreny computer has 8GB of RAM. It is using 1.4 Gb for purpose 1, with about 5 applications open (on linux, I'm sure windows would require double
), and 2.7 Gb for cache. So having more RAM would provide no speed boost. 2Gb would be sufficient, and more than 4Gb is superflous, though it means it's future proof. It has an SSD and an HDD, which applications stored on the SSD for quick loading, with personal files and content that changes a lot on the HDD (for unix users, \var and \home are on the HDD and the rest are on the SSD).
* One might ask why the computer doesn't store all of the data for purpose 1 in RAM and use anything spare for caching. Actually, this is probaby what would happen if you were going between applications frequently, but if not, the operating system will copy some of the data used for purpose 1 to the disk and use the memory saved for caching. The reason is, the memory used for caching is a copy of what's on the hard drive, so it can be deleted from RAM in a second if RAM is needed for pupose 1, rather than having to copy that to the disk first.
TLDR - if your computer frequently performs slugglishly, particularly when switching between applications, more memory would provide a large speed boost. Otherwise, it will have a small or no speed boost at all. Upgrade something else instead.
