Computer Science

• ALU (Arithmetic Logic Unit)


  • Performs arithmetic operations such as addition, subtraction, multiplication, and division
  • Compares data items (smaller, greater, equals to)
• There are thousands of LED’s (light emitting diodes) in a computer that light up to display images and text on a screen
• CPU (Central Processing Unit)


  The brain of a computer that processes everything
• Cache is small amounts of very fast memory near the CPU used to store data
• Technology is always active even if it appears “off”, e.g., connecting to the internet, uploading to the cloud
• ROM (Read Only Memory)


  Memory that cannot be changed, stores basic input and output settings, and is non-volatile
• Types of memory

  • RAM (Random Access Memory)
  • ROM (Read Only Memory)
• Multi-core processors have duplicate processors linked together on a single chip
• There are a lot of switches in a computer where 0 means off and 1 means on, binary code is important in computers as it helps perform tasks
• RAM (Random Access Memory)

  Main memory that is volatile, fast access, and can be changed
• Registers are tiny amounts of extremely small memory used to carry out specific tasks
• ‘fetch-decode-execute’ cycle

  1. Computer executes 4 billion instructions per second

  2. Fetch from main memory, decode in CPU, execute by loading and storing data onto memory then performing an operation
• Motherboard

  Connects all the pieces together and holds them in place
• CPU

  1. Heats up but the heat is drawn into thin aluminium rods and cooled by a large fan

  2. Split into 2 parts: the control unit and the ALU (Arithmetic Logic Unit)
• Cache memory

  Small amount of very fast, expensive memory in the CPU that can be accessed faster than RAM
• When RAM is filled up

  The software goes to the hard drive, which is further away and therefore takes longer to access, making the computer slower
• RAM

  • “Memory” used to temporarily hold: OS, Programs, Data currently being used by the CPU, key to increasing the computer’s performance
• 3 main types of storage

  • Magnetic, Tape, Optical, Solid state
• Solid state storage

  • Data is recorded onto solid memory chips without any physical moving parts, flash memory is non-volatile but will eventually wear out after being written 100,000 times
• Tape storage

  • Used for cold storage, large capacity and cost-effective but slow to transfer, serial access - must be read from the beginning
• Cloud storage is used to store documents and media online for easy access from another computer, often free and remotely secure
• Different storage solutions exist to keep up with changing technology
• When RAM is full

  The computer must use the hard disk space to temporarily store data and instructions
• Devices with flash memory


  • Camera, mobile phones, portable computers, USB, smart cards, SD cards
• Volatile memory

  • Loses all content when power is switched off
• Uses of secondary storage

  • Non-volatile, programs and data stored on hard disks, CDs used to distribute software, music, films, memory sticks used to transport data, magnetic tape or external hard drive used for backup
• Magnetic storage

  • Mechanical parts move over the disk's surface to read and write data magnetically, capacity of 500GB-3TB or greater
• Optical storage


  • Lasers read and write using light, CD-ROM, DVD-ROM, Blu-ray, CD-RW, DVD-RW
• Future storage could be on a strand of DNA
• Open-source software


  Used because it can be edited easily to suit your own needs and is cheaper than windows
• Haptic feedback


  The use of touch to communicate with users e.g., phone vibrations
• CPU main parts

  Control units and Arithmetic Logic Unit
• GUI


  Clearly displayed on screen using a combination of graphics and text which you can click on with your mouse
• BIOS (Basic Input Output System)

  Instructions needed for a computer to start – computer checks all the hardware, OS starts
• Encryption software


  Encrypts data so it can’t be accessed by unauthorized people
• Control unit

  Controls all the operations carried out by the computer
• Hard Disks

  1. An actuator moves the read-write arm to the correct position

  2. Read-write head is a tiny magnet that doesn’t actually touch the platter

  3. A central spindle allows the platter to rotate at high speed

  4. Each platter is divided into areas

  5. Each area can be magnetized or demagnetized to store 0 or 1

  6. A map FAT(File Allocation Table) shows where each file is and which sector is free
• RAM is key to increase a computer’s performance because it can be increased so your computer can store more instructions and data
• Types of software

  • Application
  • Program
  • Executables
  • Utility Software (e.g., antivirus, disk defragmenter, backup utility)
• Number of cores

  • 2 cores – dual core
  • 4 cores – quad core