Memory PDAs employ memory to store the operating system, standard applications and additional programs. Memory is also used for working space and data storage. More memory is usually better because it increases processing speed. However, it's difficult to compare storage capacity between models with different operating systems. One model with 4 MB of RAM could store more data than another 4 MB model with a different operating system.
Most devices already have sufficient memory to store all the personal information of a typical user.
If you want to load up on applications, look for a PDA that has upgradeable memory or supports removable storage like CompactFlash or PC Cards. The down side of adding memory is increased battery drain. Extra memory for PDAs is also more expensive than that for regular computers. You can often buy third-party memory which is less expensive, but adding more memory than the device specifies or opening the PDA case yourself can invalidate the warranty. Ergonomics PDAs come in a wide spectrum of sizes and weights, from credit card size to the dimensions of a hardcover book.