They operate the same and differ only in how the map data is stored in the unit.
The Road Mate 700 has all the data for North America pre-loaded on an internal hard drive; the 500 requires the user to load the desired data to a Compact Flash (CF) card. (There is also a difference in package contents -the 700 does not include the A/C adapter, USB data cable, and CF card found in the 500 package).
GPS devices, however, are only as reliable as the data stored on them, so they should be updated regularly.
The Road Mate is a quality product, in fact, we rate it as a breakthrough new product in that it is the FIRST Car Navigator that we have tested that is ready to operate "out of the box" as it comes.
The RM700 has a 10GB micro disk drive which has been preloaded with road maps for ALL of the USA and the southern most (high population) areas of Canada.
The unit has a jack for an external amplifies antenna.
This is a solid unit with a large, bright touch screen, great speaker, easy to use controls, and an intuitive interface.