# L5 ALU - Computer Science 230H ALU Computer Arithmetic...

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Computer Science 230H ALU – Computer Arithmetic Prepared by Michael Jack Fall 2007 Slides set 1

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ALU 2 References The information and figures for the following slides were prepared from the following source: Patterson, D., and Hennessy J., Computer Organization and Design, 3rd edition, 2005 Stallings, W., Computer Organization and Architecture: Designing for Performance 7 th edition, 2006 Hircock B., Computer Science 230 Course Notes
ALU 3 Objectives Arithmetic and Logic Unit (ALU.) Data representation formats. Computer arithmetic.

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ALU 4 Introduction The two principal concerns (that apply both to integer and floating-point arithmetic) for computer arithmetic are: – The way in which numbers are represented (the binary format.) – The algorithms used for the basic arithmetic operations (add, subtract, multiply, divide.) The Central Processing Unit (CPU) is the logical combination of the Arithmetic Logic Unit (ALU) and the system’s control unit (CU.) The ALU is that part of the computer that actually performs arithmetic and logical operations on data. All other elements of the computer system – CU, registers, memory, I/O - are there mainly to bring data to the ALU for processing or to take results back out.
ALU 5 The ALU Data are presented to the ALU in registers and the result of the operation is stored in registers. The ALU may set flags (stored in registers) as the result of an operation – E.g. an overflow flag is set if the result of a computation exceeds the length of the register into which it is to be stored. The CU provides signals that control: – The operation of the ALU. – The movement of the data into and out of the ALU.

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ALU 6 The ALU (cont) In early machines, simplicity and reliability determined the overall structure of the CPU and its ALU – The result was that machines were built around a single register, known as the accumulator. – The accumulator was used in almost all ALU related instructions. The power and flexibility of the CPU and the ALU is improved through increases in the complexity of the hardware – Use general register sets to store operands and addresses, and results. – Use special hardware to support transfer of execution between points in a
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## This note was uploaded on 02/14/2010 for the course COMPUTER S COIS-3030 taught by Professor Hircock during the Spring '10 term at Trent University.

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L5 ALU - Computer Science 230H ALU Computer Arithmetic...

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