1. 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. [Who? Where? When? Implemented using what?] 2. Immediate Access Storage. (2003-10-24)
