Measured in megabytes (MB), the more memory you have, the more applications and files you can work on at once. In order of increasing speed, the most common types of RAM are: SDRAM (synchronous dynamic RAM), DDR (double data rate) SDRAM, and RDRAM (Rambus dynamic RAM). Each memory type is available at different speeds. Regardless of the type of RAM you want, it is recommended that you get at least 256MB.