Processes (6)

Question 1

What is a program?

Answer 1

In an OS context: an inanimate entity.

In a non OS context: an animate entity.

Question 2

What else other than program code does a process contain?

Answer 2

3 memory areas: stack, main, heap. Also contains data store for variables.

Question 3

What is single user vs multi-user systems?

Answer 3

Single: only 1 process at a time, processor dedicated to that process.
Multi: several processes interleaved, reasonable response time, allocate resources, support inter-process communication, user creation of process.

Question 4

How are processes created?

Answer 4

User logs on, process spawns another process, batch job, created to support service ie printing.

Question 5

How are processes terminated?

Answer 5

Log off, quit, error, termination of batch job.

Question 6

List 7 reasons for process termination?

Answer 6

Normal completion. Time limit exceeded. Memory unavailable. Bounds violation. Protection error. Arithmetic error. Time overrun (waiting for event to happen).

Question 7

List another 7 reasons for process termination.

Answer 7

I/o failure invalid instruction. Privileged instruction. Data misuse. OS intervention (deadlock). Parent terminates so child terminates. Parent request.

Question 8

In two state process model what are two ways a process can occur to be not running?

Answer 8

Queuing for it’s turn to start. Was interrupted and is queuing for it’s turn to restart.

Question 9

What advantage has five state model over two state model?

Answer 9

Two state doesn’t distinguish between non-running processes ready to to run and non-running processes not yet ready to run.

Question 10

List five states of five state model:

Answer 10

New, ready, running, blocked, exit.

Question 11

What initiates transition from one process state to another?

Answer 11

Short-term and long-term schedulers.

Question 12

What is the solution to having jus 1 queue for blocked processes?

Answer 12

Have multiple separate queues for each event the blocked processes are waiting on.

Question 13

What two types of processes are there?

Answer 13

CPU an I/O bound processes.
Cpu mostly calculations.
I/o mostly I/o.

Question 14

What is solution to inefficiency of fast cpu and slow I/o devices?

Answer 14

Suspending blocked processes. This frees up memory for adding more processes.

Question 15

What two new states are needed to add suspending of blocked processes?

Answer 15

Blocked, suspend. Ready, suspend.

Question 16

How does a locked state become a suspend state?

Answer 16

It is swapped to disk.

Question 17

Name five reasons why process may be suspended.

Answer 17

Swapping (OS needs main memory to bring in another process), OS reason, user request, timing, parent request.

Question 18

What are constructed so OS can manage all entities of computer system? 4 examples.

Answer 18

Tables. Ow memory occupation tables, io tables, file tables, process tables.

Question 19

What 4 attributes make up a process Inge for a process table?

Answer 19

Data, program, stack(procedure calls and parameters), process control block.

Question 20

What is PCB?

Answer 20

Process control block. Attributes used by OS for process control.

Question 21

What does a PCB contain?

Answer 21

All the information about a process needed by the OS. Read by every module in the OS.

Question 22

What are the 4 categories of process information stored in the PCB?

Answer 22

ID, status (blocked etc), state and control, accounting.

Question 23

What is process accounting?

Answer 23

Info regarding how long process had cpu, how long in system, when it finished, time waiting for I/o, storage used during execution.

Question 24

What is state and control?

Answer 24

Information about process relating to register contents (whether interrupted etc), main memory (where it’s stored), resources (what’s been allocated to it), process priority.

Question 25

What five steps happen when a process is created?

Answer 25

Assign Pid, allocate space, initialize control block, set up linkages, create data structures (ie accounting file).

Question 26

What are five reasons for context switch?

Answer 26

Clock interrupt, I/o interrupt, memory fault (must bring into main memory), trap (error handling), supervisor call (OS call).

Question 27

What are 7 steps of context switch?

Answer 27

Save context of cpu registers, update PCB of current process, move process to appropriate queue, select another process, update other process PCB, update memory management data structures, restore context of other process.

Question 28

What is a thread?

Answer 28

A unit of dispatching, owned by process, sometimes called a lightweight process, shares resources of parent process, multiple threads mean processes can do more than one thing at a time.

Question 29

Give examples of following OS;

1 process + 1 thread, N processes + 1 thread per process, N processes + n threads per process.

Answer 29

1:1= MS DOS
N:1= UNIX
N:N= Windows, Linux

Question 30

What are four benefits of threads:

Answer 30

Less time to create new thread than new process, less time to terminate than process, less time to switch between threads within process, threads within process share memory and can communicate together without invoking kernel.

Question 31

What is a process?

Answer 31

A program in execution.