18 Thanks. That's the one I'm thinking of - the amount of memory you get on the same area of silicon doubles every 18 months. Apply it to the memory sizes of computers and it seems to work: in 1974 a small computer was a PDP-11/05 with perhaps 16 K bytes of memory (up to 56 K if you were lucky, IIRC). 24 years later = 16 * 18 months, a small computer is a pentiyuck PC with rather less than 2^^16 * 16 K = 1 gigabyte, but not that much less. A computer in the same market slot as the 11/05 is perhaps a Sparcstation, in which a gig of memory is by no means out of the question... Your place or mine? :-) :-) Philip.