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1.2.1
| Question | Answer |
|---|---|
| OS | operating system parts: - Device driver - File management - Utility software (e.g. encryption) - Application software - User interface - User management/security - Memory management - Multitasking - Interrupts |
| Device driver (OS) | software that tells the OS how to communicate with a device - Translates OS’s instructions to hardware-specific instructions - Ensures compatibility between different brands of peripherals |
| File management (OS) | - Loads files into the correct program to access them - Allows user to rename, delete, copy and move files - Provides a structure to the files |
| Application software (OS) | provides interaction between user + hardware (e.g. spreadsheets) |
| User interface (OS) | - GUI (graphical user interface) uses WIMP (windows, icons, menus and pointers) - CLI (command-line-interfaces) |
| User management/security (OS) | - Allows multiple accounts on one computer, retaining settings for each - User account control + firewalls keep each account safe |
| Memory management (OS) | - Paging - Segmentation - VM |
| Multitasking (OS) | resource management Allows several programs to run almost simultaneously by allocating each a time slice Scheduling: - RR - FCFS - MLFQ - SJF - SRT |
| Interrupts (OS) | Lets CPU know when a device needs attention (e.g. power supply failure, moving mouse, illegal instruction encountered, screen recording, printer ink running out Peripherals send an interrupt to the CPU with a certain priority |
| Paging (Memory management) | - Memory fully split up into pages (equally sized chunks, physically divided) - Programs may be split up and stored in different parts of memory |
| Segmentation (Memory management) | - Memory is divided into segments (not equal sizes, logical divisions) - Segments group data together is it is better to be stored together - May lead to unused memory space |
| VM (Memory management) | virtual memory: space on a hard disk - When RAM is full, data is transferred to VM - Data must go through through RAM when called by the CPU, slowing the process down |
| Scheduler (Multitasking) | manages which process, and for how long, to execute next |
| Preemptive algorithm (Multitasking) | processes can be suspended if a higher priority process joins the queue |
| Ready queue (Multitasking) | where processes waiting to be executed are stored |
| RR (Multitasking) | round robin (pre-emptive): - Each process runs for a specific period of time (time slice/quantum) - At end of quantum, process goes to back of queue, even during execution |
| FCFS (Multitasking) | first-come-first-served: - Processes served in order they arrive, each completed before moving on - New processes are added to back |
| MLFQ (Multitasking) | multi-level feedback queues (pre-emptive): Several ready queues storing different priority processes Prioritises processes w/ short CPU but high I/O bursts CPU completes highest priority queue first, and goes down list Processes can change priority |
| SJF (Multitasking) | shortest job first: - Completes process with shortest execution time first |
| SRT (Multitasking) | shortest remaining time (pre-emptive): - Shortest process done first - If shorter process joins halfway, CPU switches |
| Interrupt and FDE cycle (Interrupts) | At the end of a FDE cycle, CPU checks if there are any interrupts with a higher priority then current task, if yes: (see: Inturrupt process) If another interrupt comes with a higher priority, steps are restarted, w/ current values going to the stack |
| ISR (Interrupts) | interrupt service routine: - a block of code that handles an interrupt |
| Interrupt process (Interrupts) | - Registers contents copied to stack (area in memory) - Relevant ISR memory location copied to PC - ISR carried out - Previous data popped from top of stack |
| OS types (OS) | (can have overlaps): - distributed - embedded - multi-tasking - multi-user - real-time |
| Distributed (OS types) | Allows multiple computers to work together on one task, combining processor power |
| Embedded (OS types) | Designed for embedded systems (computer system with singular function, art of a device) Pros - Not complex - Less storage/memory space - Maximum efficiency Cons - Difficult to fix bugs - Not compatible to other devices - Limited in tasks |
| Multi-tasking (OS types) | A single processor can handle more than one task at a time by scheduling processes |
| Multi-user (OS types) | Allows multiple users to use a system at once (not just allowing several accounts) |
| Real-time (OS types) | Carry out actions instantly if urgent (e.g. hospital equipment or plane sensors) |
| BIOS | basic input output system: Initial start-up instructions stored on ROM, settings stored in flash memory so they can be changed and are non-volatile Device starts: - POST run - boot loader program (bootstrap) activated to load OS kernel into memory |
| POST (BIOS) | power-on-self-test: - checks hardware is installed correctly and that the CPU recognises them |
| Virtual machines | programs with the same functionality as a physical computer common applicatations: - Emulators - Virtual servers - Intermediate code |
| Emulators (Virtual machines) | translates hardware-specific instructions for a different system |
| Virtual servers (Virtual machines) | perform servers task + some, saving money and increasing reliability |
| Intermediate code (Virtual machines) | not CPU or human readable, stopping the need for different compilers for each device e.g. Java; translated to intermediate code, and translated by JVM (java virtual machine) at the other end |
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