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Computer Architectures Jung H Kim Dept of Systems Engineering Chapter1. Computing and Computers Elements of Computers Brain Control Execute Instruction Data (100-3)*2(100-5)/3 Data Processor Control Instruction Execute Data Data Paper Memory Input/ Output Devices Every Computer Must Have the Following Components 1. A processor capable of control and execute programs. 2. A memory for saving programs and data. 3. A means of transferring information between the memory and a processor and between the computer and outside world. Computation Z = f(x) Derived output Given input in order to evaluate f(x), express x as a sequence of function(or instruction set) f1, f2, … , fn Y1 = f1(x) Y2 = f2 (Y1) : : Y n-1 = f n-1(Y n-2) Z = f n(Y n-1) Limitation of Computers Touring Machine ( reasonable computing machine) :A function f is computable if f(x) can be executed by any specified x in a finite number of steps. P X … … Memory 1. The machine should not store the answers to all possible problems. 2. The machine should only be required to solve problems to which a solution procedure or a program can be given 3. It should process information at a finite time. Limitation of Computers Unsolvable Problem Goldbach’s conjecture : Every even integer greater than 2 is the sum of exactly two prime number such as 8=3+5 and 12=5+7. It is not known if the conjecture is true for every even integer, nor is any reasonable procedure known to determine whether the conjecture is true. Limitation of Computers Intractable Problem Factors : the nature of the given problem and computer power ) Example. Traveling sales problem The brute-force approach : n! The best algorithm : exp(n) Two questions in the difficulty of the algorithm 1.Space complexity : How much memory space is needed to execute it? 2.Time complexity : How much time is needed to execute it? The VLSI Era VLSI(Very Large Scale Integration) LSI(Large Scale Integration) MSI(Medium Scale Integration) SSI(Small Scale Integration) : profound impact on computer design and application Current VLSI : photolithography technique Ex) CPU on a VLSI chip Playstation 2 on a VLSI chip Wafer scale integration( WSI ) The VLSI Era CISC( Complex Instruction Set Computers ) Intel 80x86, Motorola 680x0 : Execution of even a small percentage of complex instructions can reduce overall performance RISC( Reduced Instruction Set Computers) IBM 6600/ SUN SPARC Von Neumann bottle neck : CPU-memory speed disparity It takes CPU about 5 times longer to obtain a word from memory than from one of internal registers -- how to reduce the bottle neck: cache memory, interleaved