Function and Purpose of OS Flashcards
What is an operating system?
The core software that controls how computer operates e.g. Windows, Linux, iOS, Android etc.
What must OS’s do?
- Control the hardware
- Manages software through loading and unloading applications from memory
- Provide security
- Provide a UI
What are are the main parts of the OS?
Kernel, Device Drivers, UI, System Utilities
What does the kernel do?
- Load and unload applications fro memory
- Schedule tasks to run efficiently on the CPU
- File and Memory management
- File storage to and from secondary storage devices
- Data security
What do device drivers do?
Every piece of hardware that communicates with the OS requires a device driver that enables internal or external device to communicate with the OS
What does the user interface do?
Allows a user to interface and interact with the computer e.g. GUI, Command Line Interface, Natural Language Interface
What do system utilities do?
Part of the OS that provides all the basic facilities that run in the background without user interaction e.g. print spool services, cryptographic password management or file management services
What is the purpose of memory management?
Without any form of memory management, recently opened programs could overwrite data and programs that were already in use, causing it to be corrupted, preventing programs and data from being overwritten
What is memory segmentation?
The allocation of segments of memory to allow a process to run and segments are not fixed sizes so will be as large as necessary to hold a process
What are the different parts of memory segments?
- Code segment stores program instructions
- Data segment stores program variables
- Stack segment stores functions + subroutines and can grow into the free memory segment
What is paging?
A page is a fixed sized division of memory, with each page being given and number and is recorded in the page table. Processes can be put into many different pages. Paging is used for virtual memory
What is virtual memory?
When the memory is full, the OS will take the least used pages and move them to the secondary storage device as virtual memory. This is extremely slow.
What is polling
Polling is the CPU or program regularly checking to see if an event or peripheral needs attention.
What are the advantages and disadvantages to polling?
Advantages:
- Very simple and predictable as only occurs at specific points while software runs
Disadvantages:
- May be inefficient in CPU processing time
What are interrupts?
A signal for the CPU to stop what it is doing and instead carry out the interrupt task
Each interrupt has a priority and if it has a higher priority than the current process, the CPU will suspend the task and performs the Interrupt Service Routine (ISR)
What happens during an Interrupt?
When an interrupt of a higher priority than the current task arrived, the CPU completed the current FDE cycle and moves everything that was in the registers to the RAM in a stack. Once the IRS is completed, the previous contents of the CPU registers are moved from the stack back to the CPU
What are the issues with interrupts?
Latency and stack overflow (when the stack grows too big when too many interrupts arrive at the same time
What is scheduling?
The task of allocating CPU time amongst all running programs
What does scheduling ensure?
Processes as many tasks as possible in a given time, make maximum use of CPU time, minimised delay, maximises use of resources, able to prioritise jobs
Name the different types of OS
Multi-tasking, Multi-User, Real Time, Distributed, Embedded
What is a multi-tasking OS?
Allows more than one program to be run concurrently relative to the user
What is a multi-user OS?
Allows multiple users on different system to access a single computer through a network e.g. an office mainframe
What is a real time OS?
Designed to handle input data within a guaranteed time and so is designed to be reliable and have consistent timing used in factory production lines and mars rovers
What is a distributed OS?
Controls a number of computers at the same time to undertake a single high resource task. Each computer contains part of the overall OS and the group is called a cluster used in render farms and super computers
What is an embedded OS?
Hardware is designed to handle a specific task on specific system hardware, used in cash machines, cars
What is a BIOS?
Basic Input Output System contains the most basic hardware settings of the computer with set of instructions to boot the computer and is stored on ROM or flash memory on the motherboard
What are the 4 stages of booting?
Power Up, POST, Hardware Checks, OS Start
What happens during the Power Up stage?
When the on button is pressed, it powers the PSU and once it is sending a steady output of power, it sends a hardware reset signal to the CPU through the control bus
What happens during POST (Power On Self-Test)
- Checks the BIOS is not corrupted
- The system chips are ok
- The CPU, DRAM and VRAM are ok
- The keyboard is present
What happens during the hardware checks?
The BIOS initialises the computer’s internal components and the order the BIOS looks for the OS is determined by the boot order in the BIOS settings
What happens during the OS start?
When the CPU boots a drive, it attempts to search for the boot sector, which is usually the 1st accessible sector of memory and runs the instructions in the boot sector which contains the Master Boot Record (MBR)
From the MBR, the BIOS finds the secondary storage device that holds the OS and from there finds the boot sector, loading the OS into the memory
After the OS is booted, the boot file is run to prepare the computer for personal usage
