'Solid-state' and 'no moving parts'. They are the phrases manufacturers use to let us know that stuff is reliable. Researchers such as Professor Asen Asenov of the University of Glasgow know, however, that solids aren't all that solid. The core problem is variability. Experts speaking at the recent international conference on CMOS Variability in London, organised by the UK's National Microelectronics Initiative (NMI), see the 22 nm process as a critical juncture in the evolution of the silicon chip. Due to start production in 2012, the process will use transistors so small that Asenov claims: "You can count the dopant atoms. You can even count the number of silicon atoms in there. The random placement of dopant atoms in the channel of a transistor can lead to big changes in performance, even between two devices sitting within tens of nanometres of each other on a die, to the extent that one works and the other a failure. Size is not the only cause of variability.