Computer Science

Computer Science

1. Data

   • Binary
     • A group of 8 adjacent bits is known as a byte.
       • Half a byte is known as a nibble.
   • Data Representation
     • The size of a bitmap image is expressed as width x height
     • A bitmap is a digital image composed of tiny blocks of colour called pixels.
     • The resolution of an image is measured in pixels per inch.
     • The colour depth of an image is the number of bits used to encode the colour of each pixel.
     • File size on a bitmap image: width x height x colour depth
     • File size of a sound file: sample rate x bit depth x duration
   • Data Storage and Compression
     • Compression algorithms reduce file sizes by repackaging or removing some of their data.
     • A lossless compression algorithm reduces file size while retaining exact meaning of the original data.
     • A lossy compression algorithm can reduce file size by up to 90% by permanently deleting some of its data.
     • File sizes are measured in kibibytes, mebibytes, gibibytes and tebibytes.
     • Each unit is 1024 times larger than the previous one.

2. Networks

   • Network Speeds
     • Speed: Refers to how much data can be downloaded per second over a connection.
       • Bandwidth: Maximum amount of data that can be transmitted over a connection per second.
     • Latency: Time taken for transmission to reach destination. Measured in milliseconds.
       • Ping is a way of measuring latency.
     • Network speed = file size (in bits) / time (in secs)

3. Computers

   • What is a computer system?
     • Consist of hardware and software.
     • Hardware: refers to physical components e.g CPU and the software is the set of programs running on the hardware.
   • Hardware
     • The stored program concept of Von Neumann: His proposed design for a new computer architecture allowed both program instructions and data to be stored together in a computer's main memory.
       • Von Neumann architecture consists of main memory and a central processing unit (CPU), interconnected by buses.
         • CPU consists of the CU, ALU and registers.
         • Buses connect the CPU with memory. There are three types: address, data and control bus.
     • Main memory, also known as RAM, consists of a collection of storage locations. Each location has its own unique memory address.
     • The clock sends out signals at intervals to all other hardware components in order to synchronise their actions. The faster the clock, the more instructions the CPU can execute per second.
   • Fetch- Decode- Execute Cycle
     • Fetch: CU puts memory address of next instruction on address bus. RAM receives signal and copies content of memory location indicated by address bus onto data bus.
     • Decode: CU decodes instruction.
     • Execute: CU sends signals to other components of CPU telling them what to do.

4. Issues and Impact

   • Environmental Issues
     • The manufacture, use and disposal of devices has a big impact on the environment.
       • E.g. creating harmful e-waste and consuming vast quantities of energy.

5. Computational Thinking and Problem Solving with Programming

   • Algorithms and programs
     • Flowcharts can be used to represent an algorithm graphically and visually.
     • Algorithms are step-by-step plans for solving problems.
       • They can be displayed as written or visual.
   • Data Types
     • Variables have data types that fit their purpose.
     • Different variable types include: string, boolean, integer etc.

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