Operating Systems

Operating Systems

1. Interrupts

   • Inerrupts are a signal for the CPU to stop what it is currently doing and carry it on after the more important task is complete
   • Every interrupt has a corresponding ISR
     • ISR- Interrupt Service Routine
       • The ISR is a set of instructions that have to be carried out when the event occurs
   • Interrupts can stop the CPU from what it is doing
     • The CPU knows which interrupt to handle first as there is a hierarchy
       • Some interrupts are more important than others
       • 1. Hardware
       • 2. Software
       • 3. Timer
       • 4. I/O Devices
         • The order of hierarchy is known as interrupt prioity

2. Componetns

   • Kernel
     • Loads and unloads applications into the memory
     • Makes sure the applications don't interfere with each other
     • Allows applications to share the use of the CPU more effiently
     • Handles file storage to and from secondary devices
   • Drivers
     • Each piece of hardware connected to a computer has a device driver
     • Drivers allow the device to communicate with the OS
     • There are normally hundreds of drivers pre installed
       • These are loaded on boot up
         • They allow us to plug our devices into the computer and they are automatically recognised
   • User Interface
     • The user interface directs what the user can see on the monitor
     • It is a direct result of any instruction they have requested to process. (the output of their request)
   • Utilites
     • Printing
     • Archiving
     • Back up
     • Antivirus
     • Antispyware
     • Password Management
     • File Management

3. Functions

   • I/O control
     • Communicate through device driver, control amount of CPU time for devices efficiently, recognise PnP
   • Task Management
     • Allocating resources to different processes to maximise CPU efficiency
   • Security
     • User areas, protected files, read/write permissions. Critical if connecting to the internet
   • Resource Management
     • RAM, virtual RAM, caches, CPU and bandwidth. Manage these to make the CPU work effiently
   • Filing
     • Create and maintain robust directory store / organise data and program files and retrieve from secondary storage
   • User Interface
     • Accepts user commands, displays messages, confirms successful input

4. Polling

   • The continuous checking of of other software or hardware by one piece of hardware or software to see what state they are usually in
   • Usually transmits a signal 1000's of times a second
   • Not an effective way of processing devices

5. BIOS

   • BIOS
   • Basic Input/Output System
   • Checks everything before running

6. UEFI

   • Unified Extensible Firmware Interface
   • Expected to eventually replace BIOS
   • Has less limitations compared to the BIOS

7. Types of OS

   • Embedded
     • The processor is integrated into a device with a specific control purpose
     • These devices are often low powered with very little RAM and storage and there is normally no need for multitasking
     • Can only be used on that device
   • Distributed
     • The power of several independent computers is combined to solve a problem via a network
     • The distributed system is presented to the user/users as a single system
   • Network
     • Connected to a server
     • Able to view files on other computers
   • Multi-user
     • More than one user can access the same data at the same time
     • Usernames and passwords needed
   • Multi-tasking
     • When a user can have more than one program loaded into the RAM
     • The more processing core the more instructions can be carried out
   • Real Time
     • The system responds to the input without delay
     • Control systems use them