Source : Free On-Line Dictionary of Computing

Intel 4004
     
         The world's first {microprocessor}, released in
        1971.  The 4004 contained 2300 transistors (compared with 5.5
        million in the 1996 {Pentium Pro}) and was intended for use in
        a calculator.  It processed data in 4 bits, but its
        instructions were 8 bits long.  Program and Data memory were
        separate, it had 1 {kilobyte} of data memory and a 12-bit {PC}
        for 4K of program memory (in the form of a 4 level {stack},
        used for CALL and RET instructions).  There were also sixteen
        4-bit (or eight 8-bit) general purpose {registers}.  The 4004
        had 46 instructions.
     
        (1997-03-30)