Operating Systems

Operating Systems

1. what does it do? it manages ...

   • all connected devices
   • RAM and virtual memory
   • running programs
   • the file system
   • security
   • network and internet connections

2. Apple

   • fast and responsive
   • innovative design na dinterface
   • very few viruses, more secure than windows
   • software and hardware can be really expensive
   • difficult to use

3. linux

   • will run on any hardware
   • very few viruses
   • free
   • not easy to use
   • you have to wait a while for someone to fix bugs

4. windows

   • most common OS, most software available
   • hardware tends to be designed with windows in mind = less problems getting hardware to work
   • very insecure, victim of most viruses
   • uses a vast amount of system resources

5. DOS

   • will run on smaller systems
   • faster system, not slowed down by graphics
   • texted based only, no user graphical user interface
   • does not support networking

6. types of operation system

   • real time OS - processes data in real time
   • Single user single task - runs one application at a tie
   • single user multi tasking - Can manage multiple applications at the same time
   • multi user - Allows several users to operate the same or different software at the same time, this would be used on a large network system where multiple users are accessing software and documents at the same time

7. OS interfaces

   • GUI - Graphical User Interface
   • WIMP - Windows, Icons, Menus, Pointers
     • windows - Each application will open up in a new windows. This can be dragged, resized or closed by the user. The image to the right shows two windows open with different applications running.
     • Icons are small images which represent a action or task within a application or OS. When the user clicks on a icon an event is sent to the application so it can deal with that event.
     • Menu’s are used to access features which may not be as well used as the ones represented by icons. A menu is split into sections (such as File, Edit, View etc) which can be further split up.

8. command based systems

   • Systems such as DOS rely on command prompts being typed in by the user
   • This requires a large amount of expert knowledge by the user and leaves no room for errors and mistakes.

9. memory management

   • Memory is shared amongst all of the programs running on your system.The OS has the responsibility to manage which program has what part of memory. This is known as memory management.
   • The memory manager is a small piece of code within the OS which will – Allocate memory to a program Will reclaim it when it is not in use Will swap memory blocks in and out of virtual memory Will prevent programs from accessing each others memory.

10. preventing hacking

    • The memory manager must stop a program from accessing other parts of memory.
    • Consider spyware running on a system. If it could have access to the web browser memory it could read all of your sensitive information. It could also over write it and even control your web browser!

11. allocating memory

    • When a program needs memory it must ask the memory manger to allocate it. The memory manager will need to decide if anything will need to into virtual memory or not.

12. greedy program

    • Sometimes a program may use up more memory than it should. The OS should prevent a single program from accessing ALL of the memory as this would prevent other processes from running

13. memory and task manager

    • You can monitor how much memory is being used on your computer. Each running program will say how much memory has been allocated to it.

14. multi-tasking

    • Multi-tasking is how the OS can run more than one program at once. It gives the illusion that programs are running concurrently while in reality they are simply taking turns on the CPU
    • This is because each core can only run one program at a time. The process of allocating tiny amounts if processor time is so fast that it appears that it is all running at the same time.

15. Device drivers - The device driver converts what the OS wants to do into messages that the devices understand.

16. issues with multi tasking

    • Swapping programs around takes time. If it is done too often then the system will slow down as too much time will be spent doing the swap!
    • If programs are not swapped often enough then the user will notice “freezes” where the screen stops responding. This is when the running program is waiting for CPU time or another device such as the hard drive.
    • Multi-tasking also makes programming harder as it can cause bugs which are unpredictable!

17. Peripheral managemnent

    • Peripheral device – A device plugged externally into the PC
    • Many different devices can be plugged into a PC. These will perform input, output and storage functions and are made by many different vendors. The OS needs to be able to communicate and manage all of these devices! No easy feat!
    • In order to communicate with hardware the OS will use device drivers. These are small programs written by the vendor to allow the OS a generic way of communicating with the hardware.