When it comes to adding system memory also known as RAM, the general rule of thumb is the more, the better.

On average, doubling the amount of memory in your system will give you ample "space" to work and make an obvious difference in overall speed, especially with today's memory-hungry applications, such as Microsoft Office programs and graphics-intensive games. You'll be able to run more programs simultaneously, and your system will be less likely to lock up or behave unexpectedly. You'll also find it easier and faster than ever to edit graphics and sound. The bottom line is that adding memory makes your computer more efficient and allows you to do more things at once.

Any time you add RAM, consider this money-saving tip. If the memory upgrade will fill all the slots in your system, get as much memory (megabytes) as you can. This will save you money if you ever want to upgrade down the road. That's because once you fill a system's slots, you have to remove some of the existing memory to make room for new, higher-capacity modules.
 

How much total memory do you need?

You know that more memory is better, but what's the absolute minimum amount of memory you need? In general, most current operating systems run best with at least 128MB of RAM, and preferably 256MB or more to take advantage of the features the OS has to offer. That's just for the operating system. Then, you need to add more memory for each additional program you plan to run at a given time. To calculate the number, look at the software you're running, and then add the amount of memory required for each application you'll likely run at one time to the amount you need for your operating system. If you're not sure how much memory your software requires, the following charts can help.

OS Software