Chapter 4 : Operating systems and computer architecture

Question 1

What are the 14 things that the operating system does?

Answer 1

1. Human computer interface (HCI)
2. Multitasking
3. Multiprogramming
4. Batch Processing
5. Error handling
6. Loading and running of applications/software
7. Management of user accounts
8. File utilities (e.g. copy, save, sort, delete)
9. Processore mangement
10. Memory management
11. Real-time processing
12. Interrupt handling routines
13. Security (manages log on, passwords)
14. Input and Output control

Question 2

a) What is an interrupt?

b) And what does it do?

Answer 2

a. An interrupt is a signal sent from a device or from software to the processor to request the processors attention if it is an error or a high priority task.
b. It will cause the processor to temporarily stop what it is doing and service the interrupt.

Question 3

When can interrupts occur?

Answer 3

1. When a disk drive is ready to receive more data.
2. When an error has occurred, such as a paper jam in a printer.
3. When the user has pressed a key to interrupt the current process - an example could be keys being pressed simultaneously,
4. When a software error has occurred - an example of this would be if an .exe file couldn’t be found to initiate the execution of a program.

Question 4

State the order of the Fetch Execute Cycle

Answer 4

1. Copy contents of PC to the MAR and initiate memory read
2. Instruction read from memory location is copied to MBR (MDR)
3. Increment the PC (go to the next instruction)
4. Copy the instruction from the MBR to the IR (CIR)
5. Decode instruction
6. Execute instruction
7. Repeat from step 1

Question 5

What does MAR stand for? - And what is its purpose?

Answer 5

Memory Address Register - hold a data or instruction address

Question 6

What does MDR stand for? - And what is its purpose?

Answer 6

Memory Data Register - temporarily holds the contents in the MAR so it can be copied to the CIR

Question 7

What does ALU stand for? - And what is its purpose?

Answer 7

Arithmetic and Logic Unit - it does bit wise and mathematical and logic operation

Question 8

What does PC stand for? - And what is its purpose?

Answer 8

Program Counter - Contains the address of the next instruction

Question 9

What does CIR stand for? - And what is its purpose?

Answer 9

Current Instruction Register - holds the current instruction

Question 10

What are the 3 types of buses?

Answer 10

1. Address Bus
2. Data Bus
3. Control Bus

Question 11

What does the Address Bus do?

Answer 11

Carries signals relating to addresses between the processor and the memory

Question 12

What does the Data Bus do?

Answer 12

Sends data between the processor, the memory unit and the input/output devices

Question 13

What does the Control Bus do?

Answer 13

Carries signals relating to the control and coordination of all activities within the computer (examples include: the read and write functions)

Question 14

What signal direction does the Address Bus have?

Answer 14

Unidirectional (signals travel in one direction only)

Question 15

What signal direction does the Data Bus have?

Answer 15

Bi-directional (data can travel in both directions)

Question 16

What signal direction does the Control Bus have?

Answer 16

This is regarded as being both unidirectional and bi-directional due to the internal connections within the computer architecture

Question 17

What is a buffer?

Answer 17

It is used in computers as a temporary memory area

Question 18

Where are buffers used?

Answer 18

They can be used to temporarily store a video while the video is being watched

Question 19

What does the control unit do?

Answer 19

It controls the operation of the memory, processor and input/output devices