Computer science 3

• Booting


  1. Part of the OS is loaded into the

  2. This is done with the help of BIOS system
• BIOS (Basic Input Output System)


  Handles the start of the computers motherboard. It tells the computer where the storage device that holds the O/S can be found, it then loads the part of the O/S that is needed and executes
• BIOS


  1. Loads part of the operating system

  2. Handles the device that holds the computer storage
• BIOS


  • Stored in a special type of ROM, called EEPROM (Electrically Erasable Programmable ROM)
  • EEPROM is a memory chip that is programmable and its contents remain even when the computer is powered down
  • The BIOS settings are stored on a CMOS chip
• Interrupt


  A signal sent from a device or software to the OS, where the OS temporarily stops what it is doing to service the interrupt
• Interrupt handling


  1. The interrupt handler deals with the signal, prioritising interrupts as they are received and placing them in a queue

  2. The current task needs to be stopped, with its status saved, before the interrupt can be serviced
• Buffering


  Interrupts allow two concurrent functions to co-exist, with data being passed in and out of memory very rapidly, allowing both functions to be serviced
• Optical storage


  • Optical storage devices read data by shining a laser beam onto the surface of plastic discs, which have a reflective coating
  • Data is written on a spiral track using a laser to make indentations called pits, with the lands (areas between pits) representing 0s
• Hard Disk Drive (HDD)


  • An electro-mechanical data storage device that uses magnetic storage to store and retrieve digital data
  • Data is stored on rapidly rotating platters and accessed in a random access manner by read/write heads on a moving arm
  • HDDs are non-volatile, retaining stored data even when powered off
• Solid State Drive (SSD)


  • A storage device that has no moving parts and retrieves data at the same rate, not relying on magnetic properties
  • Data is stored by controlling the movement of electrons within NAND chips, effectively producing 1s and 0s in millions of tiny transistors