The wikipedia page on the USRP seems to explain it pretty well: &#60;<a href="http://en.wikipedia.org/wiki/Universal_Software_Radio_Peripheral&#62;" rel="nofollow">http://en.wikipedia.org/wiki/Universal_Software_Radio_Periph...</a>. It also goes into the issue of daughterboards, although not in-depth.<p>The reason for daughterboards is given as "[...] designed to be flexible, allowing developers to make their own daughterboards for specific needs with regard to connectors, different frequency bands, etc."