# Lec03b - COMP 4300 Computer Architecture Instruction...

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1 COMP 4300 Computer Architecture Instruction Set (cont.) Dr. Xiao Qin Auburn University http://www.eng.auburn.edu/~xqin Fall, 2010

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2 Memory-Memory Architectures Instruction set: (3 operands) add A, B, C sub A, B, C mul A, B, C (2 operands) add A, B sub A, B mul A, B Example: A*B - (A+C*B) 3 operands 2 operands mul D, A, B mov D, A mul E, C, B mul D, B add E, A, E mov E, C sub E, D, E mul E, B add E, A sub E, D mem[D] mem[E]
3 Memory-Memory: Pros and Cons Pros Requires fewer instructions (especially if 3 operands) Easy to write compilers for (especially if 3 operands) Cons Very high memory traffic (especially if 3 operands) Variable number of clocks per instruction With two operands, more data movements are required

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4 Register-Memory Architectures Instruction set: add R1, A sub R1, A mul R1, B load R1, A store R1, A Example: A*B - (A+C*B) load R1, A mul R1, B /* A*B */ store R1, D load R2, C mul R2, B /* C*B */ add R2, A /* A + CB */ sub R2, D /* AB - (A + C*B) */ R1 = R1 +,-,*,/ mem[B] mem[D] R2
5 Memory-Register: Pros and Cons Pros Some data can be accessed without loading first Instruction format easy to encode Good code density Cons Operands are not equivalent (poor orthogonal) Variable number of clocks per instruction Limit number of registers

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6 Load-Store Architectures
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Lec03b - COMP 4300 Computer Architecture Instruction...

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