IAS

computer 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)