16.1 Purposes of a Operating System

Question 1

How does an OS maximize the use of resources?

Answer 1

• the OS uses scheduling to allow better utilisation of CPU time and resources.
• the direct memory access (DMA) controller frees up the CPU and allows it to carry out other tasks while the slower I/O operations are taking place.

Question 2

How does the OS hide the complexity of the hardware from the user?

Answer 2

• using GUI interfaces rather than CLI
• using device drivers
• carrying out background utilities, such as automatic virus scanning.

Question 3

Multi-tasking

Answer 3

• Managing the execution of many programs that appear to run at the same time.
• Allows computer to carry out more than one process at the same time.

Question 4

Why is process scheduling needed?

Answer 4

• Allow multiprogramming
• give each process a fair share of CPU time.
• Highest priority jobs can be executed first.
• Keep CPU busy all the time.

Question 5

Running to Ready

Answer 5

• TIme slice completed, interrupt occurs and process is moved to the READY queue.

Question 6

Ready to Running

Answer 6

• process turn to use processor, scheduler allocates CPU time to process.

Question 7

Running to Blocked

Answer 7

• the process carries out a I/O operation. Scheduler places it into the blocked queue.

Question 8

Blocked to Ready.

Answer 8

An I/O operation is ready to be completerd by the process.

Question 9

Paging

Answer 9

Reading/writing same size blocks of data to/from secondary storage when required.

Question 10

Interrupt handling

Answer 10

Transfering control to another routine when a service is required.

Question 11

Scheduling

Answer 11

Managing the processes running on the CPU.

Question 12

Virtual Memory

Answer 12

Using secondary storage to simulate additional main memory so CPU can access more memory space than available RAM.

Question 13

Difference between paging and segmentation

Answer 13

• Paging uses fixed size block of memory, segmentation uses variable.
• Paging as more risk of internal fragmentation.
• Process of paging is essentially invisible to user.

Question 14

How is paging used to manage virtual memory?

Answer 14

• Divide virtual memory into blocks of same size called pages.
• Divide RAM into frames
• both fixed size
• When a process is executed, a page table is used to translate logical to physical addresses.

Question 15

How is segmentation used to manage virtual memory?

Answer 15

• logical address space broken up into variable size blocks called segments.
• Each segment has a name and size
• Segments from logical memory are loaded into physcial memory using a segment map table.

Question 16

Explain the term disk-thrashing.

Answer 16

Problem resulting from use of virtual memory. Continuous swapping of the same pages can mean nearly all processing time is used for swapping pages, therefore reducing processing speed.