Computer Science 1.2.1

Computer Science 1.2.1

1. Operating Systems

   • Function/Purpose
     • Controls the peripherals, such as printers, scanners etc.
     • Organises memory use between programs.
     • Organises processing time between programs and users.
     • Provides an interface between the user and the computer.
     • Issues error messages should an error occur.
     • Manages the security of the system.
     • Manages the hardware of the system.
   • Types of Operating System
     • Real-Time Processing - When a computer has to react within a guaranteed time, a real-time OS is used. For example, autopilots, heart rate monitors.
     • Multi-User - Where several users can access the same system via a LAN. The more users, the slower the response time will be.
     • Distributed - Allows multiple computers to work together on a single task.
     • Embedded - Designed to run on embedded systems rather than general-purpose systems. Forms a part of a device such as a washing machine, a car or a vending machine.
     • Multi-Tasking - Can run multiple programs simultaneously.

2. Memory Management

   • Ensures that memory is used efficiently, as in that programs being currently used need to be stored without wasted space.
   • Ensures data in memory is secure, as most of the time programs shouldn't have access to the data of other programs.
   • Paging
     • Paging is where programs are divided physically into equal-sized blocks. These blocks are typically several kilobytes.
   • Segmentation
     • Segmentation is where programs are divide logically split into blocks containing modules, or routines.
   • Virtual Memory
     • Virtual Memory is the use of secondary storage as an extension of a computer's physical memory.

3. Scheduling

   • An operating system ensures that each job gets sufficient processing time. A scheduler is used to carry this out.
   • A scheduler uses a scheduling algorithm to determine how to share the time. There are 5 different systems that can be used.
   • Round Robin - Each is given the same time and if one doesn't finish it moves on to the next and that one moves to the back.
   • First Come First Served - The first process to arrive is dealt with first until it is finished. The rest are queued.
   • Shortest Job First - Picks the shortest job from the list and processes that first. Needs to know the job time in advance.
   • Shortest Remaining Time - Estimates how long each will take, and picks the one with the least amount of time, if one is added that is shorter, the scheduler switches.
   • Multi-Level Feedback Queues -

4. Interrupts, Device Drivers and BIOS

   • Interrupts
     • Interrupts are signals from different areas of the computer system being sent to the CPC requesting processing time.
     • Interrupts are handled by the ISR (Interrupt Service Routine). The ISR receives the information from the interrupt, reads it, and sends the information on what to do to the CPU.
   • BIOS
     • BIOS (Basic Input Output System) is used in a computer system when the computer first starts.
     • When the computer begins loading, the BIOS analyses where the different pieces of hardware are and if there are any issues. This is known as POST (Power On Self Test). POST, if it finds something is not right, uses beep codes that can be heard by the user, with a different beep code for each issue.
   • Device Drivers
     • Device Drivers are pieces of software that come with hardware such as graphics cards. The software allows the computer system to communicate with the new piece of hardware.
     • PnP (Plug-and-Play) is the ability to detect and configure hardware automatically without having to physically configure the hardware.

5. Virtual Machines

   • A virtual machine is software on a computer system that can emulate the functionality of another machine, often with a different operating system.