topic 2

operating system

a fundamental software that manages the computer hardware, provides common services for computer programs, and acts as an interface between users and the machine

why do we need Operating systems

it is essential for managing the hardware and software resources of a computer system.

main functions of an operating system

resource management, file management, interrupt handling, security, providing a user interface, providing utilities, providing a platform for software to run

resource management

operating systems manage the computer’s resources. They allocate resources to specific tasks and ensure they are used effectively

what computer resources does the OS manage

CPU, memory, disk drives and printers

file management

operating systems handle the storage, retrieval and manipulation of data files.

how do OS allow users to work with files

it provides a GUI of the file system that allows a user to decide which directory a file should be saved in and what the file name will be.

interrupt handling

the OS handles interrupts and processes them in a timely manner to maintain the smooth running of the system

security

OS provides various security features such as password-protected system accounts, virus scanning and file encryption

how can password protected system accounts be useful for security.

system accounts can be restricted from performing certain actions such as editing network settings or installing unapproved software

providing a platform for software to run

operating systems provide a platform on which application software can run, this is mainly by allowing software access to system resources.

providing a user interface

operating systems provide interaction in 2 ways, through a GUI or text-based via a command-line interface .

features of a GUI

windows, icons, menus, pointer

command line interface

instructions and commands are typed into the interface

file encryption

allows users to send files over networks securely

file compression

reduces the size of a file , which helps send large files over a network

disk cleanup

scans the hard disk for duplicate and corrupt files and deletes them to create ore space on the disk

memory management

fundamental role of the OS, dealing with the allocation and deallocation of the computer’s primary memory

benefits of memory management

efficient allocation of memory enables multitasking,

memory management maintains security, it doesn’t let programs access memory reserved for other programs

memory management techniques

paging, segmentation, virtual memory

paging

paging is the process of dividing the primary memory into fixed equal sized blocks called pages

advantages of paging

facilitates efficient memory management and enables the use of virtual memory

drawbacks of paging

can lead to internal fragmentation as unused space in a page is wasteful as other unrelated data can’t be stored in the page and more pockets of wasted space will exist across the memory

segmentation

a method of dividing memory into variable-sized segments based on logical parts of a process

difference between paging and segmentation

pages are physical divisions and are fixed in size, segments are logical divisions and variable in size

virtual memory

using hard drive space as an extension of ‘RAM’ . Data is offloaded to VM when Primary memory is almost full

advantages of segmentation

allows for intuitive and efficient memory access

disadvantage of segmentation

this can result in external fragmentation , as segments fill up the memory the physical gaps reduce the maximum size of new segments that can be allocated

advantages of virtual memory

allows more extensive programs to be run and facilities effective multitasking

disadvantages of virtual memory

slower to access than physical memory, which degrades performance if overused.

interrupts

a signal to the processor that stops its current task and performs a different task temporarily

groups of interrupts

hardware events or time-sensitive tasks

what happens when an interrupt occurs

the processor suspends the current program execution and transfers control to an interrupt service routine

types of interrupts

hardware interrupts, software interrupts, trap interrupts

purpose and role of interrupts

real-time event handling, device communication , multitasking

real-time event handling

hardware errors and signals from input devices

device communication

alerts from external devices

multitasking

suspending processing in one application so that the user can switch to another

hardware interrupt

generated by external devices

software interrupts

triggered by software or the operating system

trap interrupts

intentionally triggered by a program

ISR - interrupt service routine

a special function that handles a particular interrupt type.

interrupt prioritisation

the processor can acknowledge and switch to resolving a higher-priority interrupt.

nesting of interrupts

ability of processor to handle interrupts within interrupts

scheduling

deciding which tasks to process, for how long and in what order is achieved through scheduling algorithms

types of OS scheduling algorithms

round robin, first come first serve, shortest remaining time, shortest job first, multilevel feedback queues

round robin

each job is given a time slice to use the CPU. if the job has not completed by the end of its time slice, the next job is allocated a time slice

first come first serve

the first job to arrive is executed until it is completed

shortest remaining time

the time to execute each task is estimated . the job with the shortest estimated time is executed meaning that a shorter new job can take over the current process

shortest job first

the time to execute each task is estimated. the job with the smallest execution time is executed until it is completed. then the next shortest task is scheduled.

multilevel feedback queues

multiple queues are created. each queue has a different priority level. If a job uses too much CPU time, it is moved down to a lower priority queue.

benefits of round robin

• all processes get a fair share of the CPU

• good for time-sharing systems

drawbacks of round robin

• choosing the right period of time can be difficult

• can lead to high turnaround time and waiting time for longer tasks

benefits of first come, first served

• simple and easy to understand

• fair in the sense that processes are served in the order they arrive

benefits of multi-level feedback queues

• smaller tasks are prioritised

• creates a prioritisation system where similar-sized tasks are queued together

drawbacks of multi-level feedback queues

• more complex than other algorithms

• setting the correct parameters can be complicated

benefits of shortest job first

• minimises waiting time

• efficient and fast for short processes

drawbacks of shortest job first

• can cause starvation of longer processes

• requires estimation of the task in advance

advantage of shortest time remaining

• ideal for jobs that have shorter estimated times

• minimal waiting time - provides lowest average waiting time

disadvantages of shortest time remaining

• requires estimation of time to execute each task

• starvation of longer tasks

types of operating systems

distributed , embedded, multi-tasking, multi-user, real-time

distributed operating systems

run on multiple machines appearing as a single unit, used for efficient task distribution and load balancing

embedded operating systems

Designed for specific tasks, is the system running inside a device that is not primarily a computer system

multi-tasking operating systems

Allows multiple tasks to run concurrently on a single processor, manages system resources and allocates CPU time to different processes

multi-user operating systems

Supports multiple users accessing computer resources concurrently, efficiently manages resource allocation, and provides features for data security and user privacy

real-time operating systems

Designed for immediate data processing, and can ensure tasks are processed in specific timeframes, highly efficient

BIOS

basic input / output system of a computer. The first program that runs when computer system is switched on. It initialises hardware and performs a POST.

what is POST

power-on-self-test. A diagnostic testing sequence that ensures all the hardware components are working properly.

what happens if bios encounters ant errors during this test

will either halt the boot process or issue an error message

what happens if the POST succeeds

BIOS will run the bootstrap loading sequence which its the program responsible for starting the OS

device drivers

a piece of software that enables communication between an operating system and specific hardware devices by translating instructions.

why is a device driver so important

allows the OS to control and interact with different devices, and perform specific operations.

what problem can the device driver solve

the fact that every manufacturer of a device has its own standard, device drivers enables the device to communicate with various computer systems.

virtual machine

a software-based emulation of a physical computer that runs an operating system and applications

uses of virtual machines

cross-platform compatibility, software testing, legacy support

cross-platform and legacy support

not all software is designed to run on all OS, so a virtual machine of different OS can be used.

After new updates of an OS, a virtual machine of the previous OS can be used to access it

in software testing of virtual machines

VMs are a way to create isolated test environments that leaves the host OS unaffected

what do isolated environments allow a developer to do

monitor the way their software affects system performance, test on a clean-slate system while no other applications are running

what can VM management software do

create virtual machines that act like they have older hardware. This allows developers to build software that can be run on older hardware so that more users can use the software.

how else can developers use Virtual machines

to test against various oS for greater compatibility

intermediate code

code generated through compilation and allows programs to run across different OS

benefits of virtual machines

allows software to run of different OS

supports legacy applications

provides isolated test environments

drawbacks of virtual machines

uses system resources such as CPU, RAM and storage from the host machine

performance is usually slower than running software directly on physical hardware

complex to set up and manage

applications

software designed to perform a specific task or tasks for a user

utility software

software designed to help analyse, configure, optimise or maintain a computer.

utility software types

disk defragmentation, file management, device driver, system cleanup, firewall, anti-malware, compression, back up

disk defragmentation role

to rearrange files on the disc drive to increase efficiency.

file management role

software used to organize, search, rename and relocate files stored on the system

system cleanup role

software used to free up space on the system by removing unnecessary files and data.

firewall

software that manages incoming and outgoing network traffic and prevent malicious request from other devices

compression

software that reduces size of files

back up

software that automatically makes copies of specific data to cloud or physical storage

anti-malware

software that detects, quarantines and removes malicious programs

open source

software that can be used by anyone without a license and is ​distributed with the source code​.

closed source

closed source code requires the user to hold an appropriate license to use it , users cannot access the source code

benefit and drawback of open source to creator

• benefit : collaboration, community engagement and faster innovation

• drawback: less control , burdened with requests from users

benefit and drawback of closed source to creator

• benefit: greater control, revenue through sales, IP protection

• drawback: slower innovation, full responsibility for updates and flaws

benefit and drawback of open source for user

• benefit : free, customisable and transparent

• drawback : might be less user-friendly, compatibility issues and bugs

benefit and drawback of closed source for user

• benefit : more polished products, professional support and consistency in updates

• drawbacks : costly, less customisable

translator

software that converts source code from a high level language to a low level language