Jayjos, when speaking of memory its referring to download capability, the basic models, (E-Trex, Garmin72, Garmin76, As well as Magellan's 310, 315) have 1 meg of download capability (memory). Generally, the cheaper the unit, the fewer megs it will offer.
The 1 meg units will just hold waypoints and a few routes, when you get into the mapping units (Map76, 76S, Legend, Vista, and Magellans Meridian series) you'll get anywhere from 8 to 24 megs, which lets you add more detailed info to the basic maps in these units.