Those with long memories and large coat pockets may recall the “sub-notebook” PCs of the 1990s and early 2000s, such as Psion’s Series 7, Toshiba’s Libretto, Compaq’s Contura Aero and Olivetti’s Quaderno.

The concept is making a comeback as a high-performance, “ultra-portable” device that slots neatly in between full-size laptops and hybrid devices such as the HTC Shift (www.htc.com) with its tilting 7in touch screen, slide-out qwerty keyboard and built-in 3G cellular data connection.