OS Roles and functions (A1.3 Operating systems)

Operating system (OS)

- Manages computer hardware and software resources and provides common services for computer programs

- Intermediary between user and computer hardware = efficient and secure operation of system

I. ROLES

Primary roles of OS

ROLES: CPU management

Allocates CPU time to processes, ensure efficient execution

ROLES: Memory management

- Control and coordination of RAM

- Allocates memory to apps

Virtual memory (ROLES: Memory)

Memory-management technique: temporarily transfer inactive data (page/segments) from RAM to secondary (disk) storage to use more memory than physically available

- Memory management unit (MMU) - maps virtual address to physical memory

logical addresses to physical address in RAM or disk

- Physical RAM is full = OS swaps pages to move inactive pages from RAM to designated disk areas

- Paging - split memory into equal pages (sectors) to let non-contiguous segments fit in RAM

.vs Segmentation - organizing memory into variable-sized (not equal/fixed!) sections

- = execution of larger programs, multitasking

ROLES: Storage management

Organizes data on storage devices, reliable data storage and retrieval

- File management - storage (save), retrieval, organization, manipulation of data

.Structured way to manage files and directories = system stability and security

.Hierarchical file system/tree-like structure

.No 2 files in same directory may have same name

File extension (ROLES: Storage)

Suffix at end of filename that indicates file type and program associated with opening/processing file

Defragmentation (ROLES: Storage)

Reorganize fragmented data on HDD so files stored in contiguous blocks

- = ^ access speed

- Fragment - temp files scattered across different disk sectors from creating, modifying, deleting files (eg copy file creates tmp file of original file)

ROLES: Device management

Coordinate hardware devices and data transfer, provide drivers and interfaces

Device driver (ROLES: Device)

Specialized software for OS to communicate with and control hardware devices

- Plug and play (PnP) technology - OS automatically installs necessary drivers and settings (no need to do manually)

Buffering (ROLES: Device)

Use of temporary data storage (buffer) when speed mismatch between devices

- = Release same time

- Usually by RAM

- Ex: keyboard input vs CPU processing, video streaming vs display

Caching (ROLES: Device)

Store frequently used data in caches

Spooling (ROLES: Device)

Process of queuing/scheduling data/tasks in buffer,= processed sequentially

- System can work on other tasks in meantime

II. FUNCTIONS

Primary functions of OS

FUNCTIONS: Scheduling

Allocates CPU time to processes = efficient, fair system resources use

- Multitasking environments

- = optimize performance, reduce wait times, maintain system stability

- MINIMIZE:

.Response time - time for machine to respond to user input

.Waiting time - time user spends in queue waiting for that response

- MAXIMIZE:

.Throughput - # of completed processes per unit time

.CPU utilization: maximizing all resources

- see Scheduling quizlet in this folder for scheduling algorithms

Key challenges (FUNCTIONS: Scheduling)

Deadlock - 2/+ processes stuck forever, each waiting for other's resource

Thrashing - System spends most CPU time swapping pages, not doing real work

Starvation - process can't be supported by current resources (either lack of resources or resources are being dominated)

FUNCTIONS: Security

Protect confidentiality, availability, integrity of computer's resources and information so that users and applications can operate securely

User authentication (FUNCTIONS: Security)

Requires user credentials (username, password, biometric data)

- Authorization - permissions, access levels

.OS grants/prevents access based on user settings

.Access control lists (ACLs) - specifies which resources user/processes can access and can have operations

- = multi-user with different access credentials

Encryption (FUNCTIONS: Security)

Data can't be read without decryption key (even when intercepted by unauthorized)

- Eg files, communication channels, devices

Auditing and monitoring (FUNCTIONS: Security)

All system activities tracked by OS in log (auditing)

- Activities: users logging in, file access, system errors, admin actions

- = help admins detect suspicious activities and potential security breaches, identify issues and areas for improving system performance

Malware protection (FUNCTIONS: Security)

Included mechanisms to detect and prevent malware infections and intruders

- Include: antivirus software, firewalls, intrusion detection systems (IDS)

.Scan malicious software

.Monitor network traffic

.Block unauthorized access attempts

.Protect system from viruses, worms, trojans, etc

FUNCTIONS: Accounting

Monitor and manage usage of system resources

- Track resources consumption by users and processes = provide insights for system administrations

- = analyze performance, allocate costs, optimize resource utilization

Resource usage tracking (FUNCTIONS: Accounting)

CPU, memory, disk, network

Process accounting (FUNCTIONS: Accounting)

Process ID, user iD, execution time, start and end times, resource consumption

FUNCTIONS: Graphical user interface (GUI)

Allow intuitive user interaction with system (vs command line interface)

- Elements: windows, icons, buttons, cursors/pointers

Application management (FUNCTIONS: GUI)

Interaction with multiple applications

- = ^ user productivity, experience

- Task switching = move quickly between open applications

.Taskbar, application switcher (alt + tab) = efficient navigation

- Split-screen effect - snapping windows to edges/corners = multitasking

- Personalized and organized workspace: users can place icons, shortcuts, widgets in desktop environment

File and system management (FUNCTIONS: GUI)

Simplified through visual tools and interfaces

- GUI-based file management tool (eg File explorer) = navigate directories, view file properties, perform operations (copy, edit, delete, rename)

- Drag-and-drop functionality = user-friendly method to transfer data

Accessibility (FUNCTIONS: GUI)

- Screenreaders = text into speech/braille

- High-contrast themes, screen magnifiers = ^ readability for low vision

- Keyboard shortcuts = v reliance on mouse.touchpad, help limited mobility

Visual feedback (FUNCTIONS: GUI)

Helps users understand what's currently happening in system

- = ^ overall ux

- Include:

.Progress indicators - status of ongoing operations (progress bars, loading animation)

.Notifications

.Tooltips - small informative text boxes when hover over icons

Customization and personalization (FUNCTIONS: GUI)

- Widgets and gadgets - quick access to info/tools

- = ^ satisfaction and productivity

FUNCTIONS: Virtualization

Running multiple VMs (Virtual machines - computer inside a computer operate independently with own OS and apps) on single physical machine

- Why? Build IaaS, etc

Hypervisor (FUNCTIONS: Virtualization)

Software that creates VM by allowing multiple OS to run simultaneously on single physical machine (sharing hardware)

- Allocates CPU time, memory, storage to each VM

- = efficient resource use, each VM works as if on separate physical machine

Live migration (FUNCTIONS: Virtualization)

Move VM from one physical host to another without interrupting services

- = ^ load balancing and hardware maintenance

.Load balancing - process of distributing network/application traffic across multiple resources

.= ^ optimal performance,^ reliability and availability, prevent single server from being overwhelmed

FUNCTIONS: Networking

Establish and maintain network connections by managing network interfaces and protocols

- = enable devices to connect to LANs, WANs, internet

- Configures network settings