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Chapter 20

Chapter 20. Computer Operations. Computers operate according to a set of instructions stored in the main memory. The steps involved in the processing of an instruction is called the instruction cycle. The coding system used is the machine code. 20.1 Functions of and

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Chapter 20

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  1. Chapter 20 Computer Operations

  2. Computers operate according to a set of instructions stored in the main memory. • The steps involved in the processing of an instruction is called the instruction cycle.

  3. The coding system used is the machine code.

  4. 20.1 Functions of and Interconnection between Computer Hardware Components

  5. Central Processing Unit (CPU) • It controls all the other components in the computer.

  6. It contains THREE main components: • Control unit (CU) • Arithmetic and logic unit (ALU) • Registers

  7. Control Unit • It sends and receives control signals to and from peripheral devices. • It interprets the instructions stored in main memory.

  8. It regulates the timing of all operations performed within the CPU. • It sequences the instructions to be executed. • It controls the flow of data between the CPU, main memory and peripheral devices.

  9. Three Main Components of the Control Unit • Instruction Register (IR) • It holds the current instruction fetched from main memory.

  10. Instruction Decoder • A logic circuit which interprets the current instructions stored in the instruction register. • Program Counter (PC) • It holds the address of the next instruction to be accessed.

  11. Control unit Main memory +1 PC 01 02 03 READ A 04 READ B 05 06 Instruction decoder IR 03 READ A

  12. Arithmetic and Logic Unit • It performs addition, subtraction, multiplication, division and decision making.

  13. Two Main Components of the Arithmetic and Logic Unit • Accumulator (ACC) • A register which temporarily holds the intermediate or final result of arithmetic and logic operations.

  14. Status Register (SR) • It describe the status of the current contents of the accumulator and holds a collection of bits.

  15. Main Memory • It contains RAM, which is composed of a large number of memory locations.

  16. Four Main Components of Memory Unit • Main Memory • Memory Address Register (MAR) • It holds the addresses of the data or instructions to be accessed.

  17. Memory Data Register (MDR) • It holds the data or instructions read from or written to the main memory. • Address Decoder • It interprets the address held in the MAR.

  18. Control unit Memory unit +1 Main memory PC MAR 01 02 03 READ A 04 READ B 05  Instruction decoder IR Address decoder MDR 03 03 READ A READ A

  19. Buses • It is a group of wires that is interconnected throughout the computer. • It is used to communicate among all components of the computer.

  20. Three Main Types of the Buses • Data Buses • They are lines which send data signals. • The number of lines represents the number of bits of the data.

  21. Address Buses • They are lines which send address signals of the data to be processed. • The more the address lines, the more the memory locations that can be addressed.

  22. Control Buses • They are lines which send control signals from the control unit to other parts of the computer. • The number of lines varies in different computer system.

  23. The interconnection of buses within components of a computer

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