Computer+Architecture+Module+1.2.pptx

Computer Architecture and Organization Module 1.2 – Computer Evolution and Performance History The ENIAC (Electronic Numerical Integrator And Computer), designed and constructed at the University of Pennsylvania, was the world’s first general purpose electronic digital comput...

Computer Architecture and Organization Module 1.2 – Computer Evolution and Performance History The ENIAC (Electronic Numerical Integrator And Computer), designed and constructed at the University of Pennsylvania, was the world’s first general purpose electronic digital computer. The project was a response to U.S. needs during World War II specifically for the army’s Ballistics Research Laboratory (BRL). History The stored-program concept, where program could be represented in a form suitable for storing in memory alongside the data was developed by John von Neumann. Alan Turing developed the idea at about the same time. The first publication of the idea was in a 1945 proposal by von Neumann for a new computer, the EDVAC (Electronic Discrete Variable Computer). History Von Neumann and his colleagues began the design of a new stored program computer, referred to as the IAS computer, at the Princeton Institute for Advanced Studies, which is the prototype of all subsequent general-purpose computers. History A main memory, which stores both data and instructions An arithmetic and logic unit (ALU) capable of operating on binary data A control unit, which interprets the instructions in memory and causes them to be executed Input and output (I/O) equipment operated by the control unit Von Neumann Machines With rare exceptions, all of today’s computers have this same general structure and function and are thus referred to as von Neumann machines. The memory of the IAS consists of 1000 storage locations, called words, of 40 binary digits (bits) each. Both data and instructions are stored there. Numbers are represented in binary form, and each instruction is a binary code. Each number is represented by a sign bit and a 39-bit value. A word may also contain two 20-bit instructions, with each instruction consisting of an 8-bit operation code (opcode) specifying the operation to be performed and a 12-bit address designating one of the words in memory (numbered from 0 to 999). IAS Memory Formats Registers Memory buffer register (MBR): Contains a word to be stored in memory or sent to the I/O unit, or is used to receive a word from memory or from the I/O unit. Memory address register (MAR): Specifies the address in memory of the word to be written from or read into the MBR. Instruction register (IR): Contains the 8-bit opcode instruction being executed. Instruction buffer register (IBR): Employed to hold temporarily the righthand instruction from a word in memory. Program counter (PC): Contains the address of the next instruction-pair to be fetched from memory. Accumulator (AC) and multiplier quotient (MQ): Employed to hold temporarily operands and results of ALU operations. For example, the result of multiplying two 40-bit numbers is an 80-bit number; the most significant 40 bits are stored in the AC and the least significant in the MQ.