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Penn CIS 240 - Welcome Aboard

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Chapter 1Welcome AboardBased on slides © McGraw-HillAdditional material © 2004/2005/2006 Lewis/Martin 1-2CSE 240Computer System: Layers of AbstractionSoftwareHardwareApplication ProgramLanguageInstruction Set Architecture (and I/O Interfaces) MicroarchitectureCircuitsDevicesAlgorithms1-3CSE 240Recurring ThemesAbstraction• Allows us to manage seemingly insurmountable complexity• One billion components require abstractionHardware v. Software• Separation of hardware and software is artificial1-4CSE 240Recurring Theme #1: AbstractionAbstraction hides detailsExamples• “Turn off the light!”• “Stick out your tongue.”Computing examples• Java methods• C functions• LC-3 instructions• Logical gates• TransistorsBottom line• Often best to operate at highest level of abstraction• Dangerous to completely ignore lower levels of abstraction1-5CSE 240Recurring Theme #2: Hardware v. SoftwareArtificial distinctionGreatness arises from blurring the HW/SW line• CISC vs RISC (complex vs “reduced” instruction set computing)• MMX/SSE• Intel’s Itanium - EPIC (explicitly parallel instruction computing)• Research proposals: RAW/Trips. . .Bottom line• We really care about computation• Hardware best understood by those who know software• Software best understood by those who know hardware1-6CSE 240Very Big IdeasUniversality• All computers can compute the same thing*Layered Abstraction• We can build very complex systems from simple components1-7CSE 240Big Idea #1: Universal Computing DeviceAll computers can computing exactly the same things**given enough time and memory= =PDAWorkstationSupercomputer1-8CSE 240Turing MachineMathematical model of a device that can performany computation – Alan Turing (1937)• Ability to read/write symbols on an infinite “tape”• State transitions, based on current state and symbolEvery computation can be performed by someTuring machine. (Turing’s thesis)Tadda,b a+bTuring machine that addsTmula,b a*bTuring machine that multiplies1-9CSE 240Universal Turing MachineTuring described a Turing machine that could implementall other Turing machines• Inputs: data, plus a description of computation (Turing machine)Ua,b,cc(a+b)Universal Turing MachineTadd, TmulU is programmable – so is a computer!• Instructions are part of the input data• A computer can emulate a Universal Turing Machine,and vice versaTherefore, a computer is a universal computing device!1-10CSE 240From Theory to PracticeIn theory• Computers can compute anything that’s possible to compute• Given enough memory and timeIn practice• Solving real problems requires computing under constraints!“engineering” constraints• Time! Weather forecast, next frame of animation, ...• Cost! Cell phone, automotive engine controller, ...• Power! Cell phone, handheld video game, ...1-11CSE 240Big Idea #2: Layered AbstractionHow do we solve a problem using a computer?• Systematic sequence of transformations between layers of abstraction. . .ProblemAlgorithmProgramSoftware Design:choose algorithms and data structuresProgramming:use language to express designInstr SetArchitectureCompiling/Interpreting:convert language tomachine instructions1-12CSE 240Deeper and Deeper…Instr SetArchitectureMicroarchCircuitsProcessor Design:choose structures to implement ISALogic/Circuit Design:gates and low-level circuits toimplement structuresDevicesProcess Engineering & Fabrication:develop and manufacturelowest-level components(transistors)1-13CSE 240Descriptions of Each LevelProblem Statement• Stated using "natural language"• May be ambiguous, impreciseAlgorithm• Step-by-step procedure, guaranteed to finish• Definiteness, effective computability, finitenessProgram• Express the algorithm using a computer language• High-level language, low-level languageInstruction Set Architecture (ISA)• Specifies the set of instructions the computer can perform• Data types, addressing mode1-14CSE 240Descriptions of Each Level (cont.)Microarchitecture• Detailed organization of a processor implementation• Different implementations of a single ISALogic Circuits• Combine basic operations to realize microarchitecture• Many different ways to implement a single function(e.g., addition)Devices• Properties of materials, manufacturability1-15CSE 240Many Choices at Each Level“Solve a system of equations”Gaussian eliminationJacobiiterationRed-black SOR MultigridFORTRAN C C++ Javax86SPARC PowerPCIntel Pentium 4 Pentium D AMD Athlon 64Ripple-carry adder Carry-lookahead adderCMOS Bipolar GaAsTradeoffs:costperformancepower(etc.)1-16CSE 240Course OutlineBits and Bytes• How do we represent information using electrical signals?Digital Logic• How do we build circuits to process information?Processor and Instruction Set• How do we build a processor out of logic elements?• What operations (instructions) will we implement?Assembly Language Programming• How do we use processor instructions to implement algorithms?• How do we write modular, reusable code? (subroutines)I/O, Traps, and Interrupts• How does processor communicate with outside world?C Programming• How do we write programs in C?• How do we implement high-level programming constructs?1-17CSE 240Next TimeLecture• Chapter 2: Bits and BytesReading• Chapter 2 - 2.5Quiz• Don’t forget!Upcoming• Homework 1 due on Friday, September


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