Computer science

• Secondary memory


  Storage of computer data
• Types of secondary storage

  • Hard disk drive (HDD)
  • Solid state drive (SSD)
  • Memory sticks/Flash memories (pen drives)
• Hard disk drive (HDD)

  • Electro-mechanical storage device that uses magnetic storage to store and retrieve digital data using one or more rigid rapidly rotating platters coated with magnetic material
  • Data accessed in a random access manner, meaning that individual blocks of data can be stored and retrieved in any order
  • Non-volatile, retaining stored data even when powered off
  • Data read/written as the magnetic dots pass under the read/write heads
• Solid state drive (SSD)

  • No moving parts, all data accessed at the same rate
  • Don't rely on magnetic properties, most common type store data by controlling the placement of electrons with NAND chips, data stored as 1's and 0's in millions of tiny transistors within the chip
  • Effectively produces a non-volatile, rewriteable memory
• Memory sticks/Flash memories (pen drives)

  • Use SSD technology, usually connect to a computer through USB port
  • Very small, can be used as a backup device for music or photos, lightweight and suitable for transferring files between computers
• Dongle


  A small hardware device that connects to a computer to enable the use of certain software, the software won't work properly without the dongle, preventing copying of the software
• Complex or expensive software such as an expert system may offer use of memory sticks and dongles
• Digital camera


  • Lens, image sensor, and image processing system which can automatically control settings like speed, aperture and focus
  • Image sensor is an array of millions of light-sensitive devices (CCD) which convert light into electric charge, each sensor is referred to as a pixel
  • Analogue-to-digital converter (ADC) converts the electric charges from each pixel into levels of brightness, also measures colour to produce a digital image file
• Keyboard


  Has a membrane of circuit board at the base of the keys, a key press completes the circuit and the computer determines which key has been pressed, referring to an index file to identify the corresponding ASCII character
• How a digital camera works

  1. Light passes through the lens

  2. Light hits the image sensor, an array of light-sensitive devices (pixels)

  3. Pixels convert light into electric charges

  4. Analogue-to-digital converter (ADC) converts the electric charges into levels of brightness and colour to form a digital image
• How a keyboard works

  1. Key is pressed

  2. Key contacts the bottom conductive layer

  3. Key contacts the insulating layer, completing the circuit

  4. Computer determines which key has been pressed

  5. Computer refers to index file to identify the corresponding ASCII character
• Optical mouse


  • Uses a red LED that bounces light off the surface
  • The reflection is picked up by a CMOS sensor
  • The CMOS generates electric pulses to represent the reflected red light
  • Digital signal processor works out the coordinates of the mouse based on the changing image patterns
• Optical mouse vs. mechanical mouse

  Optical mouse has less dust/dirt collection, more precision, generally faster than mechanical mouse
• RAM (Random Access Memory) stores temporary information used by programs while they are running.
• The CPU (Central Processing Unit) is responsible for executing instructions, performing calculations, and controlling data flow within the computer system.
• Floppy disks store small amounts of data temporarily.
• Hard disk drive stores large amounts of data permanently.
• ROM (Read Only Memory) contains permanent instructions needed to start your PC or run software applications.
• A hard disk drive (HDD) is a non-volatile storage device that uses magnetic media to store large amounts of data.
• Hard Disk Drive (HDD)


  An electro-mechanical storage device that uses magnetic storage to store and retrieve digital data using one or more rigid rapidly rotating platters coated with magnetic material. Data is accessed in a random access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are non-volatile, retaining stored data even when powered off. Data is read/written as the magnetic dots pass under the read/write heads.
• Magnetic storage


  A type of data storage technology that uses magnetism to store and retrieve digital information. It is commonly used in hard disk drives (HDDs) and magnetic tape.