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The CPU and the fetch-decode-execute cycle

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レッスンノート

What the CPU does

  • The central processing unit (CPU) is the "brain" of a computer. It fetches instructions from memory, decodes them and executes them.

Components

  • ALU (arithmetic logic unit): performs calculations and logical comparisons.
  • Control unit (CU): directs the operation of the CPU, controlling the flow of data and instructions.
  • Registers: very fast storage inside the CPU: program counter (PC) (address of the next instruction), memory address register (MAR), memory data register (MDR), accumulator (ACC) (stores results).
  • Cache: small, very fast memory close to the CPU holding frequently used data.

CPU components

CPU components

The fetch-decode-execute cycle

  • Fetch: the PC's address is copied to the MAR; the instruction at that address is fetched into the MDR; the PC increments.
  • Decode: the control unit decodes the instruction.
  • Execute: the instruction is carried out (the ALU may calculate).

Fetch, decode and execute

Fetch, decode and execute

Performance

  • Clock speed (GHz: cycles per second), number of cores (more can run tasks in parallel), and cache size affect speed.

Multiple processor cores

Multiple processor cores

Von Neumann architecture

  • Instructions and data are stored in the same memory. Embedded systems (e.g. washing machine controller) are dedicated computers.

スライド

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練習問題

無料プレビュー — 33問中8問。すべて見るには登録を。
  1. 1.What does CPU stand for?

    Easy
    • Acentral processing unit
    • Bcentral program unit
    • Ccomputer processing unit
    • Dcore processing utility
  2. 2.What does ALU stand for?

    Easy
    • Aarithmetic logic unit
    • Ball logic unit
    • Canalogue logic unit
    • Darray logic unit
  3. 3.What does the control unit do?

    Easy
    • Adirects the flow of data and instructions
    • Bperforms calculations
    • Cstores files
    • Ddisplays output
  4. 4.What is a register?

    Easy
    • Aa small, fast storage location in the CPU
    • Ba hard drive
    • Ca network card
    • DRAM
  5. 5.What is cache memory?

    Easy
    • Asmall, very fast memory close to the CPU
    • Bslow storage
    • Ca hard drive
    • Da printer
  6. 6.What does the PC hold?

    Easy
    • Athe address of the next instruction
    • Bthe result
    • Cthe current data
    • Dthe clock speed
  7. 7.What does the MAR hold?

    Easy
    • Athe address of the memory location being accessed
    • Bthe data
    • Cthe instruction
    • Dthe result
  8. 8.What does the MDR hold?

    Easy
    • Adata transferred to or from memory
    • Bonly a memory address
    • Conly the clock frequency
    • Donly the result of every addition

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