Operating Systems

Question 1

Operating system

Answer 1

to allocate the shared system resources to the executing programs

a collection of program which makes it easier for us to use a computer

a simpler abstraction of the underlying hardware (hides the complexity of hardware)

Question 2

Hardware

Answer 2

basic computing resources, cpu etc

Question 3

Operating system

Answer 3

controls and coordinates use of hardware amongst application and uses

Question 4

Application programs

Answer 4

ways in which the system resources are used to solve computing problems, compilers, text editors, email clients, webs browsers, games

Question 5

Users

Answer 5

people, machines and other computers

Question 6

Uniprogramming

Answer 6

Ability to only conduct one program at a time

Question 7

Multi-programming

Answer 7

Executing multiple programs on the same CPU giving the user the impression that these programs are running at the same time but in reality they are running one after the other

There must be enough memory to hold the OS (resident monitor) and one user program

When one job needs to wait for the I/O the processor can switch to the other job which is likely not waiting for the IO

Question 8

Time sharing system

Answer 8

Principle objective is to minimise response time

Question 9

Bootstrap program

Answer 9

Small piece of software stored in the memory area which kicks in and loads the system when you press the power button to turn your laptop on

Question 10

ROM

Answer 10

Read-only Memory

Question 11

EEPROM

Answer 11

Erasable Programmable Read-Only Memory

Question 12

Firmware

Answer 12

Create some processes

Question 13

System processes

Answer 13

Actives tasks or instances of programs, often initiated or interacted with by users

Question 14

System daemons

Answer 14

Processes in the background, running at all times regarding of whether the user is executing something or not

Question 15

Registers

Answer 15

A type of memory, very small but very fast

Smallest one on the cpu

Question 16

Main memory

Answer 16

Much larger, relatively slow, every system needs to have it

CPU can load instructions only from memory meaning any programs to run must be stored there

Question 17

Secondary storage

Answer 17

Goes away when machine is switched off, magnetic disks, optical disks, tapes (external devices)

Question 18

Cache memory

Answer 18

Data that has been used a lot is cashed into a faster storage system

If the CPU is looking for information, cache is first checked

Question 19

Storage Structure

Answer 19

• Memory is an array of bytes, each byte has its own address

Memory interaction via load/store instructions

Question 20

Load Instructions

Answer 20

Moves byte from main memory to an internal register within the CPU

Question 21

Store memory

Answer 21

Writing of a byte from CPU register to main memory

Question 22

Large portion of OS code dedicated to managing I/O devices

Answer 22

Without having any I/O devices you won’t be able to program or give anything from the outside world to the system and vice versa

Question 23

Local Buffer Storage

Answer 23

Temporary memory area within a system or device that is used to store data temporarily while it is being transferred between components, processed or waiting to be used.

Question 24

Device Driver

Answer 24

Typically downloaded

Whenever a user program wants to issue a command to a device, this will send the command to the OS.

The OS will give the command to the DD who will transfer this to the disk controller.

Question 25

I/O Mechanisms - Programmed I/O

Answer 25

Processor controls the I/O device, constantly test the status and transfer the data

Question 26

I/O Mechanisms - Interrupt Driven I/O

Answer 26

Tell the device to do an activity, and the device will announce the CPU once this is done. This allows the CPU to do some activity in the mean time.

Interrupt driven is fine for moving small amounts of data

Not really suitable for bulk data movement such as disk I/O

Question 27

I/O Mechanisms - Direct Memory Access

Answer 27

DMA - the controller transfers data directly from the I/O device to memory

• No intervention by the CPU during the transfer
• Only one single interrupt is generated, much better than one interrupt per byte, the CPU is freed up to do other perhaps more interesting tasks
• Highly efficient for bulk or frequent transfers

Question 28

Single-processor system

Answer 28

One CPU

Question 29

Multiprocessor systems

Answer 29

more than one processors, share a number of resources i.e share bus clock memory and peripherals

benefit - if one processor or cpu does not work properly you can still make use of the remaining one, although the process might be slower it will still work (this is called graceful degradation)

Question 30

What is part of an operating system?

Answer 30

System Programs - Program loader, command interpreter

Language processors - C compiler, assembler, linker

Utilities - Text editor, terminal emulator

Subroutine libraries - Standard C library, maths library

Question 31

System Calls

Answer 31

A call you make to an operating system

Typically written in a high-level language (C or C++)

Question 32

Application Programming Interface

Answer 32

Specifies a set of functions that are available to an application programmer

Includes the parameters passed to each function

Also includes the return values that the programmer can expect

Output - number of bytes read, if successful
If -1 is a failure