chap13-14 - William Stallings Computer Organization and...

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William Stallings Computer Organization and Architecture Chapter 13 Reduced Instruction Set Computers (RISC)
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& X‚ & ±kq & ±kq ²9 ♥☛ ( 9 , ) 8 9
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Major Advances in Computers (1) W&&& Solid State RAM ( * ) Cache memory  Pipelining:  ( 2 ) 1 ♥☛ RISC “* Microprocessors Microporgrammed control unit Family concept: IBM System/360, 80x86-Pentium
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Major Advances in Computers (2) W&&& Multiple processors:  multicore processors:  8 “* 8
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Another idea - RISC Reduced Instruction Set Computer Key features Large number of  general purpose  registers Limited and  simple instruction set Emphasis on  optimising  the instruction  pipeline
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Comparison of processors P463
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Semantic gap   Difference between operations in HLL and in machine language HLL--Execution inefficiency, excessive machine program size, compiler complexity Increasingly complex high level languages Large instruction sets, More addressing modes, Hardware implementations of HLL statements (case ) way1 Simple instruction sets, Less addressing modes, Optimise statements most often used way2
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Intention of CISC x ª & ± Support more complex HLLs Ease compiler writing Improve execution efficiency Complex operations in microcode
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Driving force for RISC Look for a different approach  Make architecture simpler Improve execution efficiency by optimising  statements most often used Investigate the aspects of computations.
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Execution Characteristics Operations performed Operands used Execution sequencing Studies have been done based on programs  written in HLLs Dynamic studies are measured during the  execution of the program
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Operations Assignments Movement of data Conditional statements (IF, LOOP) Sequence control Procedure call-return is very time consuming Some HLL instruction lead to many machine  code operations
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Relative Dynamic Frequency   Dynamic  Machine Instruction Memory Reference   Occurrence (Weighted) (Weighted)   Pascal  C Pascal  C Pascal  C Assign 45 % 38 % 13 13 14 15 Loop 5 % 3 % 42 32 33 26 Call 15 % 12 % 31 33 44 45 If 29 % 43 % 11 21 7 13 GoTo - 3 % - - - - Other 6 % 1 % 3 1 2 1 use registers use register sets Optimize pipeline number of instructions x k%
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Operands Mainly  local   scalar variables Optimisation should concentrate on accessing  local variables   Pascal C Average Integer constant 16 % 23 20 Scalar variable 58 % 53 55 Array/structure 26 % 24 25
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Procedure Calls Very time consuming Depends on number of parameters passed Depends on level of nesting Most programs do not do a lot of calls followed  by lots of returns Most variables are local (c.f. locality of reference)
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chap13-14 - William Stallings Computer Organization and...

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