I've got a "fundamental computer concepts" book which gives the following rough guide:
Type - word size - cycle time - memory - cost - example
Home microcomputer - 8 bits - microseconds - 64k - $1000 - Apple IIc
Professional microcomputer - 16 bits - a microsecond - 256k - over $2000 0 IBM PC
Minicomputer - 16 bits - 250 nanoseconds - 512k - $10000+ - DEC PDP-11
Mainframe - 32 bits - 50 nanoseconds - 4Mb - $100000+ - IBM 3083
Supercomputer - 64 bits - 10 nanoseconds - 4+Mb - $1million+ - Crax X-MP/2
And it's copyrighted as recently as 1986 :-o
