1.2.1 Systems Software

Question 1

What’s…

OS?

Operating System

Answer 1

Programs providing user interface

Question 2

What’s…

OS’s purpose?

Operating System

Answer 2

User communicate with computer to perform low level tasks involving the management of computer memory and resources.

Question 3

In what devices are operating system essential?

Answer 3

1. Laptops
2. Mobile phones
3. Games consoles

Question 4

What are examples of desktop operating systems?

Answer 4

1. Windows
2. MacOS
3. Linux

Question 5

What are examples of desktop operating systems?

Answer 5

1. Android
2. iSO

Question 6

What features does an OS provide?

Answer 6

1. Memory management
2. Resource management (scheduling)
3. File management (moving, editing, deleting files and folders)
4. Input/ Output management (device drivers)
5. Interrupt management
6. Utility software (disk defragmenter, backup, formatting etc.)
7. Security (firewall)
8. User interface

Question 7

What’s…

3 mameory management techniques?

Answer 7

1. Paging
2. Segmentation
3. Virtual memory (VM)

Question 8

What’s…

Paging?

(1/3)

How used?

Answer 8

Memory split into equal sized pages.

Programs consist of certain no. pages.

Pages swap from main memory & hard disk as needed.

Question 9

What’s…

Segmentation?

(2/3)

How works?

Answer 9

Memory split into logically sized segments.

Split based on program’s code structure. e.g. conditional statements, loops

Question 10

What’s…

VM?

Virtual Memory (3/3)

Used when?

Answer 10

Section of hard drive used as RAM.

If main memory = insufficient space.

Question 11

What’s…

Moved into VM?

Virtual Memory

Answer 11

Unused programs

Through paging

Question 12

What’s…

Disk thrashing?

Answer 12

Computer freezes as high page swapping frequency. = More time spent transfering pages than spent running program.

Worsening as VM fills.

Question 13

What’s…

Interrupts?

Answer 13

Signals sent by software/hardware telling processor a process needs attention.

Different interrupts have different prioritys.

Question 14

How are…

Interrupts stored?

Answer 14

Priority order within priority queue inside interrupt register.

Question 15

How does…

OS service interrupts?

Operating System

Answer 15

Fairly, using Interrupt service routine.

Question 16

How does…

ISR work?

Interrupt Service Routine

Answer 16

1. Processor checks interrupt register at end of FDE cycle.
2. If interrupt priority > process being executed = special purpose registers’s contents temporarily transferred into stack.
3. Appropriate ISR loaded into RAM & flag set = signaling ISR begun.
4. Interrupt serviced & flag reset.
5. Interrupt queue checked against originally executed process.
6. Repeat untill all priority interrupts serviced.
7. Stack contents transfered back & FDE cycle resumes.