Introduction, Virtulization CPU, memory

Question 1

What happens when a program runs?

Answer 1

It executes instructions.

Question 2

Describe Von Neumann model of computing

Answer 2

The processor fetches an instruction from memory, decodes it (figures out which instruction this is), and executes it (adding two numbers, check a condition..), then processor moves to then next instruction until program completes.

Question 3

Why does the OS virtulize resources?

Answer 3

Make the system easier to use

Question 4

What does it means when the OS virtualize a resource?

Answer 4

The OS takes a physical resource, and transform it into a more general, powerful and easy to use virtual form of itself.

Question 5

What is OS often refered or known as?

Answer 5

Virtual machine, resource manager, supervisor, master control program, standard library

Question 6

Standard library to application OS provides

Answer 6

System calls

Question 7

Resources of the system

Answer 7

CPU, memory, disk

Question 8

What is it we call virtualizing the CPU?

Answer 8

Turning a single CPU or small set of them into a seemingly infinite number of CPUs and thus allowing many programs to seemingly run at once.

Question 9

What is a policy of the OS?

Answer 9

Policies are used in many different places within an OS to tell OS what to do, which program should run?

Question 10

How do modern system vision memory?

Answer 10

Array of bytes

Question 11

Through which types of instruction do program access its datastructures in memory?

Answer 11

Loads, stores or other explicit instruction that access memory. Instruction is in memory aswell.

Question 12

Explain what virtualizing of memory means

Answer 12

Each process accesses its own private virtual address space, which the OS maps onto the physical memory of the machine.

Question 13

Give an example of concurrency problem

Answer 13

When two threads tries to increment a shared variable at the same time the result will be undeterministic because the incremention of the variable isnt happen atomiclly. The loading of the variable value onto a register, incrementing it and storing it. We doesnt have anything that locks this critical section and thus the threads can go between eachother and the resulting value of the variable is unpredictable.

Question 14

Software in the operating system that manages the disk is called

Answer 14

File system

Question 15

What is the file systems responsibilities?

Answer 15

It is responsible for storing any files the user creates in a reliable and efficient manner on the disks of the system.

Question 16

What system calls are routed to the part of the operating system called the file system??

Answer 16

open(), write(), close()

Question 17

How does the OS access devices of the system

Answer 17

Through its system calls.

Question 18

Storing files, making them safe over long term

Answer 18

Persistently

Question 19

Same time

Answer 19

concurrent

Question 20

Basic goals of OS

Answer 20

Build abstractions, provide high performance (minimize the overheads of OS), protection between application, reliability, energy-effiency, security against malicious application, mobility (run on smaller devices)

Question 21

Types of overheads:

Answer 21

Extra time (more instructions), extra space

Question 22

Key to protection

Answer 22

Isolation

Question 23

Set of libraries of commonly-used functions.

Answer 23

Features of early OS

Question 24

As a number of jobs were set up and then run in a batch. One at a time.

Answer 24

Batch processing

Question 25

Difference between a procedure call and system call

Answer 25

System call transfers control into the OS while simultaneously raising the hardware privilege level.

Question 26

Mode user application run in

Answer 26

User mode

Question 27

What does it mean for an application to run in user mode

Answer 27

Hardware restricts what applications can do, cant initiate an I/O request to the disk.

Question 28

What happens when a system call is initiated?

Answer 28

Often is initiated through a special hardware instruction called trap. The hardware transfers control to a pre-specified trap handler and raises the privilege level to kernel mode. In kernel mode OS has full access to the hardware and can initiate an I/O request or make memory available to a program. When the OS is done servicing the request, it passes control back to user via a special return-from-trap instruction (which revers to user mode and passing control back to where the application left off.

Question 29

What is multiprogramming?

Answer 29

An early operating system, runs a part of a program then another and so on, switch between processes

Question 30

What is minicomputer?

Answer 30

Early type of computer, less expensive, UNIX was developed on this type of computer.

Question 31

Early operating system that took a cooperative approach to job schedulig, computer could get stuck in an infinite loop forcing reboot.

Answer 31

Mac OS (v9 and earlier)

Question 32

Features that made UNIX popular

Answer 32

Providing a compiler for the new C programming language.

Question 33

Operating system which borrowed heavily on the principles behind UNIX but not the code base and was apart of modern open-source software movement.

Answer 33

Linux, created by Linus Torvalds.