04-computer-architecture

04-computer-architecture - Introduction to Computer...

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Unformatted text preview: Introduction to Computer Architecture CSE 110: Introduction to Computer Science Brief Outline of Topics Elements of a CPU The execution cycle Complications: pipelining & branch prediction The memory hierarchy Machine instructions CPU Elements The CPU is the brains of the computer Contains a control unit, registers, and ALU Control unit coordinates CPU activity ALU performs all arithmetic/logical operations Registers store data currently in use CPU is connected to memory via a bus Execution Cycle 1. Next instruction is FETCH-ed from memory Program counter (PC) holds address of next instruction 2. Instruction is DECODE-d CPU determines what to do 3. Instruction is EXECUTE-d by ALU 4. WRITEBACK: registers are updated Program execution time = # of instructions # of stages Pipelining The standard execution cycle is inefFcient While one stage is active, the other stages are idle Solution: Always have multiple instructions in the midst of execution As you execute one, decode a second and fetch a third Program execution time = # of instructions + # of stages - 1 Branch Prediction Pipelining poses a problem where branches (jumps) are concerned By the time we decide whether or not to branch, weve already loaded several other instructions Ignoring/clearing them wastes CPU time Branch prediction tries to guess which set of subsequent instructions to fetch Uses statistical methods We also shufFe instructions to postpone branches Memory Hierarchy...
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04-computer-architecture - Introduction to Computer...

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