Basic Operating system Knowledge

Question 1

Need of an Operating system?

Answer 1

1. provides a virtual machine which could hide hardware details, providing user with an interface to application software.
2. Manages computer recourses by keeping track of them and granting permission to access them
3. Process management and Execution of applications
4. Identification of faults and troubleshooting
5. File management

Question 2

The evolution of OS?

Answer 2

1. Simple Batch system
2. Multi programmed batch system
3. Time sharing system
4. Mutli programmed time sharing sysytem

Question 3

Simple Batch System?

Answer 3

functions done batch by batch- one after another- serial processing

No direct access with the computer

When the current program ends being executed, it is written to a magnetic strip and then the OS loads the next program

Uni programming-one at a time

High response time

Question 4

Multi Programmed Batch system?

Answer 4

Memory is partitioned to hold multiple programs

When current processor is doing input output, OS switches processors and executes another program in memory

This was introduced to minimize idle time of the system

If memory is large enough to keep more programs processor could even be 100% busy

The central theme of modern OS

Question 5

Categorization of OS?

Answer 5

1. Single user-single task
2. Single user- multi task
3. Multi user- multi task
4. Real time OS

Question 6

Single user- single task

Answer 6

Occupies much less space in memory

however, it is uni programmed to do one task at a time

Question 7

Single user- Multi Task

Answer 7

Highly productive
however, complex
and occupies more space

eg; Microsoft Windows

Question 8

Multiuser- Multi task

Answer 8

Time efficient
productive- User does not have to provide instructions to every desktop. The change done to one is enough
However, space consuming
If the server is broken, cant perform from any device

These programs run on a single network- a terminal server

Question 9

Real time OS

Answer 9

To provide quick predictable responses, within specific timings
Embed systems not hardware

very fast
no need to be loaded from memory so time saving
Occupies less space in memory as well

Used in- Airplane reservation systems
Air traffic control signals
Stock involved systems
Systems with the need of instant updates

Question 10

What is a process

Answer 10

A program in execution. Or a program that can be assigned to a processor to be executed

Question 11

Reasons for process creation?

Answer 11

• When a new batch job is presented- when OS is prepared to take new work, it reads the next sequence of job control commands
• Interactive Login
• OS providing a service- creates a process to provide a function demanded by the user
  eg: a process to control printing

*To exploit parallelism- OS can spawn many processes

Question 12

Process requirements?

Answer 12

1. The ID
2. Executable code- A complied machine readable translation to be loaded to memory
3. Execution contexts- pc, waiting for I/O or not
4. Data needed for execution

Question 13

Reasons for process termination?

Answer 13

• Normal termination
• memory access violation
• process requirements not being provided
• termination of parent process
• execution time limit being exceeded
• an execution error

Question 14

Interrupts?

Answer 14

Interrupts temporally terminates an ongoing process
An interrupt can be planned- requested or unplanned- due to a
time expiry
service request
I/O completion

for example- When a disk driver is finished transferring data it may generate an interrupt to the OS to inform that its over

Interrupts occur asynchronous to the ongoing activities