The Basics of RAM
Imagine RAM as the top of your desk, your hard drive as a filing cabinet and you as the central processing unit (CPU). When you are working on something you would go to your filing cabinet, take out a file, place it on your desk and begin to work on it. Now if you go to the filing cabinet and take out five or six files and put them all on your desk at once, you will be able work much faster since you are saving the time it takes to go to and from the filing cabinet. So, the bigger the desk you have the more files your desk can hold. This is the same for RAM: the more RAM you have, the faster your CPU can work.
RAM stands for Random Access Memory, and it temporarily stores the data you are working on by copying it from your long term storage on the hard drive. If you have too little RAM your computer will have poor performance and run much slower than it should.
Many virtual private server (VPS) hosts offer a hard limit of RAM, which means the amount of RAM is fixed, and once it is used up your application will fail.
Other VPS hosting companies offer a combination of guaranteed RAM and burstable RAM. Burstable RAM refers to RAM that is unused by the VPS sites sharing the physical server and is made available to cover short-term spikes in memory uses experienced by your site or others hosted on the same server. Burstable RAM gives you an assurance that your application will not fail if at times the amount you need is greater than the guaranteed RAM, but the burstable RAM is not guaranteed to be available at all times.
Some hosts offer DDR/DRAM, especially for dedicated server hosting. DDR refers to double data date RAM, which means that both sides of the memory chip are used. DDR2 and DDR3 have more pins on the chip and hence provide faster data access speeds.
DRAM is dynamic random access memory, which is the usual type of RAM. The alternative type is static random access memory, or SRAM, which is more expensive but provides a faster access speed than DRAM because unlike DRAM data does not need to be constantly refreshed. DRAM is structurally simpler than SRAM, which allows it to achieve higher densities.
The type of RAM matters much less than how much of it you have, especially if you have a dedicated server, because the amount of RAM is fixed (but can generally be upgraded to more RAM fairly easily). If your website is popular and has many visitors, you will need more bandwidth and more RAM than if your site is small or has less traffic.
The operating system also uses RAM, so if you are using a Windows server you will need more RAM (for the graphic user interface) than you will if you are using Linux as your operating system.
The golden rule is that you can never have too much RAM, but you can definitely have too little.