Lecture6 - CSE 220 Computer Organization Memory John Von...

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CSE 220 – Computer Organization Memory John Von Neumann, Source: http://www.indwes.edu/Faculty/bcupp/lookback/ias.jpg Stored Program Computer • Also called a John Von Neumann Machine • This is what CPU datapaths are based on •P r em i s e : – both a program’s data and a program’s instructions are saved within the same memory device(s) SO – data & instructions both have memory addresses
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Executing Programs • CPUs use an Instruction cycle – also known as the ‘Fetch –Decode –Execute cycle’ • Makes use of other important registers: – PC: program counter – IR: instruction register – MAR: memory address register – MDR: memory data register – Accumulator • used for partial results of calculations 4 John von Neumann Machine PC IR ACC Input Output Devices ALU : Arithmetic and Logic Unit Control Unit 4096 Locations (words) PC Program Counter IR Instruction Register Memory …………………… …………………………………………. .
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PC & IR • Program Counter (PC) – holds the address of the next instruction to be fetched for execution – must be updated each cycle • Instruction Register (IR) – holds the instruction currently being executed • Note, in a 32-bit word system, most of the time if the instruction currently in IR came from memory address A, then PC stores A + 4 – What would be an exception to this? 6 John von Neumann Machine • For example, a high level language statement X=A+B would be translated as follows. Load A Copy A to accumulator Add B Add contents of B Store X Store contents of Acc to location X Program Area Data Area Load A Add B Store X Memory Locations A B X
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Remember, instructions are stored in memory
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This note was uploaded on 12/12/2010 for the course CSE 220 taught by Professor Staff during the Spring '08 term at SUNY Stony Brook.

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Lecture6 - CSE 220 Computer Organization Memory John Von...

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