Computer Science IGCSE

• Hardware categories


  • Input devices
  • Processing devices
  • Storage devices
  • Output devices
• Examples of input, output, and storage devices


  • Input devices: Keyboard, Mouse, Microphone, Touch screen, Interactive White Board, Digital camera, 2D scanner, 3D scanner, Bar code reader, Quick Response (QR) Code reader, Sensor

  Output devices: Screen / Monitor, Projector, 2D cutter, 3D cutter, Touch screen, Interactive White Board, Printer, 3D printer, Speaker, Actuator

  Storage devices: Hard Disk Drive (HDD), Solid State Drive (SSD), USB flash memory, Compact Disk (CD), Digital Versatile Disk (DVD), Blu-ray disk (BD), Random Access Memory (RAM), Read Only Memory (ROM)
• Central Processing Unit (CPU)


  An integrated circuit that acts as the brain of the computer, plugs on the computer's motherboard, requires a fan to keep it cool, also known as the processor or microprocessor, processes data, executes instructions, performs arithmetic and logical calculations, controls the operation of the different parts of the computer
• Microprocessors can be found in many devices beyond just computers
• Input devices


  • e reader
  • Quick Response (QR) Code reader
  • Sensor
  • Screen / Monitor
  • Projector
  • 2D cutter
  • 3D cutter
  • Touch screen
  • Interactive White Board
  • Printer
  • 3D printer
  • Speaker
  • Actuator
• Central Processing Unit (CPU)

  An integrated circuit that acts as the brain of the computer
• CPU


  • Plugs on the computer's motherboard
  • Requires a fan to keep it cool
  • Also known as the processor or microprocessor
• Functions of CPU


  1. Processes data

  2. Executes instructions

  3. Performs arithmetic and logical calculations

  4. Controls the operation of the different parts of the computer
• Where can we find microprocessors


  • Smartphones
  • Smartwatches
  • Washing Machines
  • Televisions
  • Toys
  • Digital Alarms
  • Microwaves
• Factors that affect CPU performance


  • Number of cores
  • Cache size
  • Clock speed
• Number of cores


  • The CPU may be made up of one or more processing units, called cores
  • Each core can process instructions independently
  • The more cores in the CPU, the higher is its ability to execute several instructions in parallel
  • Doubling the number of cores does not automatically double the computer's speed, as some of the speed is wasted on communication between the cores
• Cache size


  • It is a type of storage built inside the CPU itself
  • Stores frequently used data and instructions
  • Cache is used to speed up access to data and instructions
  • The bigger the size of the cache, the more data and instructions that can be stored in it, and the faster the CPU will become
• Clock speed


  • Refers to the maximum number of instructions a CPU can execute in one second
  • Measured in hertz (Hz), megahertz (MHz), or Gigahertz (GHz)
  • The clock speed can be increased by accessing the BIOS (Basic Input/Output System), which is known as overclocking
  • Increasing the clock speed may lead the computer to overheat and cause instruction execution to become unsynchronized, causing the computer to crash frequently
• Why the CPU requires the RAM while processing data


  • The CPU doesn't access the data and programs directly from the hard disk
  • It copies the required data and programs from the hard disk and puts them into the RAM
  • Reading and writing data from/to the RAM is so much faster than reading and writing data directly from the hard disk
  • The RAM holds all the data and programs required by the CPU
  • The RAM is often referred to as the Immediate Access Store (IAS)
• Components of the Von Neumann architecture


  • The concept of a central processing unit (CPU or processor)
  • The CPU is able to access the main memory (RAM) directly
  • Computer memories could store programs as well as data
  • Stored programs are made up of instructions which are executed in sequential order
• Components of the Von Neumann architecture


  • Control Unit
  • Arithmetic Logic Unit
  • Registers
  • Program Counter (PC)
  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
  • Current Instruction Register (CIR)
  • Accumulator (ACC)
  • Buses
• Control Unit


  • Sends control signals to tell the other components in the computer what to do
  • Manages the fetch-decode-execute cycle
  • Manages the transfer of data and instructions within the CPU
  • Fetches an instruction from memory
  • Decodes an instruction (i.e. change it to electrical signals / binary) using an instruction set
• Arithmetic Logic Unit


  • Performs arithmetic (e.g. +, −, shifting) operations on data
  • Performs logic (e.g. NOT, AND, OR) operations on data
• Registers


  • Memory locations that store a small amount of data
  • May be 8, 16, 32, or 64 bits in size
• Program Counter (PC)


  Stores the address of the next instruction to be fetched/read
• Memory Address Register (MAR)


  Stores the address of the memory location currently being read from or written to
• Memory Data Register (MDR)


  • Stores data read/fetched from memory/RAM
  • Stores data which is about to be written to memory/RAM
• Current Instruction Register (CIR)


  Stores the current instruction being decoded and executed
• Accumulator (ACC)


  Temporarily stores ALU calculations/data
• Buses


  • The various CPU components are connected by hair-thin communication paths called buses or bus lines
  • Address Bus: Carries memory addresses from the CPU to other components
  • Data Bus: Carries the data that must be transferred between the CPU and other components
  • Control Bus: Carries signals from the control unit (CU) to all the other CPU components
• The fetch-decode-execute cycle


  1. Fetch: Locate the instruction and retrieve it

  2. Decode: Convert the instruction to a signal (binary)

  3. Execute: Perform the commands in the instruction
• Instruction Set


  • A list of all the machine-code instructions that can be processed by a CPU
  • Any instruction is made up of an opcode and an operand
  • Includes data transfer instructions, arithmetic and logic operations instructions, and control of flow instructions
• Embedded systems


  • Combination of hardware and software built into a device
  • Designed to carry out a specific or a dedicated function or task
• Characteristics of embedded systems


  • Has a microprocessor
  • Has dedicated hardware
  • User normally cannot reprogram
  • Does not require much power
  • Cheap to manufacture
  • Works without human intervention
  • Small in size
  • Runs on firmware
  • Can be controlled remotely by a mobile phone
  • Works in a real-time (i.e. very fast reaction to changing input)
• Operation of a mouse


  1. The mouse shines a red light from a Light-Emitting Diode (LED) underneath the mouse

  2. The light reflects back from a surface through a lens in the mouse

  3. The light is converted to a binary value

  4. This value is transmitted to the computer

  5. The computer then determines the direction and speed of the movement
• Operation of a keyboard


  1. When the user presses a key on a keyboard, the key pushes a switch on the circuit board

  2. This completes a circuit

  3. Signals are sent to the computer

  4. The computer uses the data to calculate which key was pressed
• Touch screen technologies


  • Resistive
  • Capacitive
  • Infrared
• Resistive touch screen


  • Uses multiple layers of material (an upper layer of polyester and lower layer of glass) with a small space in between
  • When the top layer is touched, the top layer and the lower layer complete a circuit
  • Signals are then sent out which are interpreted by a microprocessor to determine the coordinates of where the screen was touched

  
• Capacitive touch screen


  • Uses many layers of glass that act like a capacitor, which creates an electric field between the layers from all the four corners of the screen
  • When the top-layer glass is touched, sensors detect a change in the electric field
  • The coordinate where the screen was touched is calculated by the microprocessor
• Infrared touch screen


  • Uses glass as screen material
  • A pattern of infra-red beams is emitted
  • The sensors detect where the screen has been touched through a break in an infra-red beam
  • The position where the screen touched is calculated by the microprocessor
• Characteristics of touch screens


  • Made up of two materials (glass and polyester)
  • Made up of one material (glass)
  • Good screen visibility in sunlight
  • Allows multi-touch capabilities
  • Cannot be used while wearing gloves
  • Uses the electrical properties of the human body
  • May be affected by magnetic fields
  • The most expensive to manufacture
  • The cheapest to manufacture
  • Has the least response time
  • Can be used with bare fingers
  • Can be used with stylus/pen
• Interactive White Board (IWB)


  • A large interactive display that connects to a computer
  • A projector projects the computer's screen on the IWB's surface
  • Considered as an input and an output device at the same time
  • Users control the computer using a pen, finger
  • The user can write on the IWB
  • Everything written on the IWB can be saved
  • Any application that runs on a computer can be used on an IWB
• 2D scanner vs. 3D scanner


  • 2D scanner: An input device used to scan and convert hard copies of documents and images into a digital format that can be stored and edited on a computer
  • 3D scanner: An input device used to scan a 3D object and produce a 3D digital model that can be stored and edited on a computer
• How a 2D scanner operates


  1. (Scanner) shines a light onto the surface of the document

  2. The reflected light is captured

  3. The scanner uses mirrors and lenses

  4. The captured image is converted into a digital file

  5. The digital file is a 2D image or document that can be edited on the computer
• How a 3D scanner operates


  1. Scanner shines a laser (or light) over the surface of a 3D object

  2. The scanner records the length, width, and height, (dimensions) of the object

  3. The measurements are converted into a digital file

  4. The produced 3D digital model can be edited using CAD programs or printed using a 3D printer