When is an Ultra Mobile PC not an Ultra Mobile PC? Answer: when it's Sony’s VAIO VGN-UX1XN. Microsoft may have coined the term Ultra-Mobile PC (UMPC for short) and companies like Samsung, ASUS, Gigabyte and Medion are happy to work with it, but Sony, for one, is ploughing an independent furrow. Although the company is pointedly not calling the VAIO VGN-UX1XN an 'official' UMPC, its web site states clearly that the system is a ‘high-end Ultra-Mobile revolutionary concept representing a new generation of devices’. Whatever you want to call it, this is a very small and compact computer running Windows Vista — but is it any good?