topic 4 - operating system & computer architecture

Question 1

what does an operating system do? (6)

Answer 1

• loads software
• Manages hardware
• Manages error handling
• Manages user accounts
• Allows multitasking
• Provides an interface

Question 2

how does interrupt work (4)

Answer 2

1. A signal sent to the processor
2. Requests processor time
3. Processor stops to service interrupt
4. Interrupts have different priorities

Question 3

name 3 devices that use interrupt

Answer 3

• Printer
• Keyboard
• Mouse

Question 4

name the 3 buses

Answer 4

• Control bus
• Address bus
• Data bus

Question 5

what does a Control bus do (3)

Answer 5

• Carries signals
• Directs the CPU
• Can be unidirectional or bidirectional

Question 6

what does an Address bus (2)

Answer 6

• Carries address locations of next item to be fetched

- Data travels one way ( unidirectional)

Question 7

what does a Data bus(2)

Answer 7

• Carries data that is being processed

- Data travels in both directions (bi-directional)

Question 8

name the 5 registers used

Answer 8

• PC; Program Counter
• MAR; Memory address register
• MDR; Memory data register
• CIR; Current instruction register
• ACC; Accumulator

Question 9

role of the control unit (4)

Answer 9

• Controls operation of memory, processor and input/output
• Fetches each instruction in turn
• Interprets instructions
• Sends signals to other components telling them what to do

Question 10

role of the ALU (arithmetic logic unit) (3)

Answer 10

• Carries out calculations
• Carries out logic operations
• Holds values during calculations in a register called an accumulator (ACC)

Question 11

explain the stored program concept

Answer 11

• Programs / instructions are stored in memory
• Data is stored in memory
• Instructions are fetched and executed one after another

Question 12

explain how execute fetch system operates (6)

Answer 12

1. PC has address of next instruction to fetch
2. PC copied to MAR via address bus
3. Instruction copied from memory to MDR
4. Instruction copied from MDR to the CIR
5. Value in PC incremented to point at next instruction to fetch
6. Address of instruction placed in MAR
   Instruction decoded and executed