Source : Free On-Line Dictionary of Computing

IAS
     
         The first modern computer.  It had main
        {registers}, processing circuits, information paths within the
        {central processing unit} and used {Von Neumann}'s
        {fetch-execute cycle}.
     
        The IAS machine's basic unit of information was a 40 bit
        {word} and the memory had 4096 words.  A word stored in memory
        could represent either an instruction or data.  Each IAS
        instruction was twenty bits long, so that two instructions
        could be stored in each 40-bit memory location.  Each
        instruction consisted of an 8-bit {operation code} and a
        12-bit address that could identify any of 2^12 locations that
        may be used to store an {operand} of the instruction.
     
        The {CPU} consisted of a data processing unit and a program
        control unit.  It contained various processing and control
        circuits along with a set of high-speed {registers} for the
        temporary storage of instructions, memory addresses and data.
     
        The main actions specified by instructions were performed by
        the arithmetic-logic circuits of the data processing unit.  An
        electronic clock circuit was used to generate the signals
        needed to synchronise the operation of the different parts of
        the system.
     
        (1996-11-24)