Week 3/4

Question 1

Virtualizing the CPU

Answer 1

creates an illusion that many virtual CPUs exist when there is only one physical CPU

Question 2

Time Sharing

Answer 2

A technique that allows users to run concurrent processes. Allows the resource to be used by ONE entity for a short time and then another entity and so on.

Question 3

Space Sharing

Answer 3

Resources are divided in space among the processes who want to use it.

Question 4

Mechanisms

Answer 4

Low-level machinery / Low-level methods or protocols that implement a functionality

Question 5

Context Switching

Answer 5

The underlying mechanism of saving (and restoring) the state of a process..

gives OS the ability to stop running a program and start running another on a CPU.

Question 6

Policies

Answer 6

algorithms for making a decision within the OS.

Question 7

Machine State

Answer 7

what a program can read or update when its running. Some components include:
Memory
I/O information

Question 8

Program Counter (PC)

Answer 8

tells us which instruction of the program will execute next

Question 9

How does process creation work?

Answer 9

1.Load code to any static data
2.OS allocates memory for the stack and heap
3.OS does initialization tasks like I/O streams
4.Run the program through main()
—————————-

Another Answer (for LINUX):

1. using fork() to create a parent/child process
2. using exec() on the child process to transform the process intoanything the user wants
3. First process (init) started by the kernel

Done w/ the help of a process tree

Question 10

Loading data history (Early vs Now)

Answer 10

Early times: loading processes were done eagerly (all at once)
Now: loading processes are done lazily (loads data only as needed)

Question 11

3 Process States

Answer 11

Running: currently executing instructions
Ready: process is ready to run
Blocked: not ready to run because another event is taking place (such as an I/O operation). This allows the OS to run a different process.

Question 12

Scheduled

Answer 12

When a process is moved from ready to running

Question 13

Descheduled

Answer 13

When a process is moved from running to ready

Question 14

Other Process States

Answer 14

Initial and Final (Zombie) States

Question 15

Process List

Answer 15

contains information about all the processes in the system, each entry is found in a process control block (PCB). Allows the OS to track pieces of info

Question 16

The process Tree Model

Answer 16

Organizing processes in trees where:
- each process has a parent, that can have 0 or more children.
- When the parent terminates, all children terminate
- If the child terminates the parent continues running

Question 17

Who starts the first process?

Answer 17

init in Linux

Question 18

What are system calls/syscalls

Answer 18

basically a function created by the OS.

wrappers take care of issuing syscalls
Meaning the calls themselves dont execute the function but the syscalls inside the actual function after it is called.

Question 19

How to create a start of a simpel shell that reads commands

Answer 19

while (TRUE){
type_prompt();
read_command(command,parameters);

}