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Understanding CPU Operation and Design Features

Explore CPU instruction and execution cycles, compare CISC and RISC CPUs, learn about semiconductor-based microprocessors, and delve into CPU registers and instruction sets.

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Understanding CPU Operation and Design Features

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  1. Chapter Goals • Describe CPU instruction and execution cycles • Explain how primitive CPS instructions are combined to form complex processing operations • Describe key CPU design features, including instruction format, word size, and clock rate • Describe the function of general-purpose and special-purpose registers Systems Architecture, Fifth Edition

  2. Chapter Goals (continued) • Compare and contrast CISC and RISC CPUs • Describe the principles and limitations of semiconductor-based microprocessors Systems Architecture, Fifth Edition

  3. Systems Architecture, Fifth Edition

  4. CPU Operation • Control unit • Moves data and instructions between main memory and registers • Arithmetic logic unit (ALU) • Performs computation and comparison operations • Set of registers • Storage locations that hold inputs and outputs for the ALU Systems Architecture, Fifth Edition

  5. Actions Performed by CPU Systems Architecture, Fifth Edition

  6. Systems Architecture, Fifth Edition

  7. Instructions and Instruction Sets • Instruction • Lowest-level command • A bit string, logically divided into components (op code and operands) • Three types (data movement, data transformation, sequence control) • Instruction sets • Collection of instructions that a CPU can process Systems Architecture, Fifth Edition

  8. Systems Architecture, Fifth Edition

  9. Data Movement Instructions • Copy data (MOVE) among registers, primary storage, secondary storage, and I/O devices Systems Architecture, Fifth Edition

  10. Data Transformations • Implement simple Boolean operations (NOT, AND, OR, and XOR) • Implement addition (ADD) • Implement bit manipulation (SHIFT) • Logical shift • Arithmetic shift Systems Architecture, Fifth Edition

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  12. Systems Architecture, Fifth Edition

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  14. Systems Architecture, Fifth Edition

  15. Sequence Control Operations • Control the next instruction to be fetched or executed • Operations • Unconditional branch • Conditional branch • Halt Systems Architecture, Fifth Edition

  16. Complex Processing Operations • Implemented by appropriate sequences of primitive instructions • Represent combinations of primitive processing operations • Represent a tradeoff between CPU complexity and • Programming simplicity • Program execution speed Systems Architecture, Fifth Edition

  17. Instruction Set Extensions • Additional instructions required when new data types are added • Some include instructions that combine data transformation with data movement Systems Architecture, Fifth Edition

  18. Instruction Format • Template describing op code position and length, and position, type, and length of each operand • Vary among CPUs (op code size, meaning of specific op code values, data types used as operands, length and coding format of each type of operand) • Most CPUs support multiple instructional formats Systems Architecture, Fifth Edition

  19. Systems Architecture, Fifth Edition

  20. Systems Architecture, Fifth Edition

  21. Instruction Length Systems Architecture, Fifth Edition

  22. Reduced Instruction Set Computing (RISC) • Uses fixed length instructions, short instruction length, large number of general-purpose registers • Generally avoids complex instructions, especially those that combine data movement and data transformation • Simpler but less efficient than CISC (Complex Instruction Set Computing) Systems Architecture, Fifth Edition

  23. Clock Rate • Number of instructions and execution cycles potentially available in a fixed time interval • Typically measured in thousands of MHz(1000 MHz = 1 GHz) • Rate of actual or average instruction execution is measured in MIPS or MFLOPS • CPU cycle time – inverse of clock rate • Wait state Systems Architecture, Fifth Edition

  24. CPU Registers • Primary roles • Hold data for currently executing program that is needed quickly or frequently (general-purpose registers) • Store information about currently executing program and about status of CPU (special-purpose registers) Systems Architecture, Fifth Edition

  25. General-Purpose Registers • Hold intermediate results and frequently needed data items • Used only by currently executing program • Implemented within the CPU; contents can be read or written quickly • Increasing their number usually decreases program execution time to a point Systems Architecture, Fifth Edition

  26. Special-Purpose Registers • Track processor and program status • Types • Instruction register • Instruction pointer • Program status word (PSW) • Stores results of comparison operation • Controls conditional branch execution • Indicates actual or potential error conditions Systems Architecture, Fifth Edition

  27. Word Size • Number of bits a CPU can process simultaneously • Increasing it usually increases CPU efficiency, up to a point • Other computer components should match or exceed it for optimal performance • Implications for system bus design and physical implementation of memory Systems Architecture, Fifth Edition

  28. Enhancing Processor Performance Systems Architecture, Fifth Edition

  29. Systems Architecture, Fifth Edition

  30. Range of Possible Approaches for Multiprocessing • Duplicate circuitry for some or all processing stages within a single CPU • Duplicate CPUs implemented as separate microprocessors sharing main memory and a single system bus • Duplicate CPUs on a single microprocessor that also contains main memory caches and a special bus to interconnect the CPUs Systems Architecture, Fifth Edition

  31. The Physical CPU • Electrical device implemented as silicon-based microprocessor • Contains millions of switches, which perform basic processing functions • Physical implementation of switches and circuits Systems Architecture, Fifth Edition

  32. Switches and Gates • Basic building blocks of computer processing circuits • Electronic switches • Control electrical current flow in a circuit • Implemented as transistors • Gates • An interconnection of switches • A circuit that can perform a processing function on an individual binary electrical signal, or bit Systems Architecture, Fifth Edition

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  35. Electrical Properties Systems Architecture, Fifth Edition

  36. Systems Architecture, Fifth Edition

  37. Processor Fabrication • Performance and reliability of processors has increased with improvements in materials and fabrication techniques • Transistors and integrated circuits (ICs) • Microchips and microprocessors • First microprocessor (1971) – 2,300 transistor • Current memory chip – 300 million transistors Systems Architecture, Fifth Edition

  38. Systems Architecture, Fifth Edition

  39. Microprocessors • Use small circuit size, low-resistance materials, and heat dissipation to ensure fast and reliable operation • Fabricated using expensive processes based on ultraviolet or laser etching and chemical deposition Systems Architecture, Fifth Edition

  40. Current Technology Capabilities and Limitations • Moore’s Law • Rate of increase in transistor density on microchips doubles every 18-24 months with no increase in unit cost • Rock’s Law • Cost of fabrication facilities for chip generation doubles every four years • Increased packing density • Electrical resistance Systems Architecture, Fifth Edition

  41. Systems Architecture, Fifth Edition

  42. Systems Architecture, Fifth Edition

  43. Future Trends • Semiconductors are approaching fundamental physical size limits • Technologies that may improve performance beyond semiconductor limitations • Optical processing • Hybrid optical-electrical processing • Quantum processing Systems Architecture, Fifth Edition

  44. Optical Processing • Could eliminate interconnection and simplify fabrication problems; photon pathways can cross without interfering with one another • Eliminating wires would improve fabrication cost and reliability • Not enough economic incentive to be a reality yet Systems Architecture, Fifth Edition

  45. Electro-Optical Processing • Devices provide interface between semiconductor and purely optical memory and storage devices • Gallium arsenide (both optical and electrical properties) • Silicon-based semiconductor devices (encode data in externally generated laser light) Systems Architecture, Fifth Edition

  46. Quantum Processing • Uses quantum states to simultaneously encode two values per bit (qubit) • Uses quantum processing devices to perform computations • Theoretically well-suited to solving problems that require massive amounts of computation Systems Architecture, Fifth Edition

  47. Summary • CPU operation • Instruction set and format • Clock rate • Registers • Word size • Physical implementation • Future trends Systems Architecture, Fifth Edition

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