comp sci

• Registers

  • Extremely small, extremely fast memory located in the CPU
  • Each register has its very own specific purpose
• Hard Disk Drive (HDD)

  • 500GB - 8TB (consumer-grade)
  • Low cost per GB
• Solid-State Drive (SSD)


  • 128GB - 2TB (consumer-grade)
  • High cost per GB
• USB Flash Drive

  Solid State
• USB Flash Drive

  • 8GB - 256GB (common sizes)
  • Moderate cost per GB
• CD/DVD/Blu-ray Disc

  • CD: 700MB, DVD: 4.7GB - 9GB, Blu-ray: 25GB - 50GB
  • Low cost per disc
• Binary number


  Used by computers to represent data
• Bit


  The smallest unit of data a computer can store
• Unit of data


  A term given to describe different amounts of binary digits stored on a digital device
• Converting between units


  1. Division, moving up in size of unit

  2. Multiplication, moving down in size of unit
• When dealing with all units bigger than a byte we use multiples of 1000
• When dealing with bits and bytes the same process is used with the value 8 as there are 8 bits in a byte
• All data must be converted to binary before a computer can understand and process it
• Representing data in binary


  • Magnetic hard drives use North and South polarity
  • Optical disks use light reflection
• Changing a computer system to have more options than binary

  Would be less efficient and require more complex parts
• Data capacity


  The maximum amount of information that a storage device can hold
• Calculating capacity requirements

  1. Know the capacity of the storage device

  2. Calculate the size of a file

  3. Ensure the same units of data storage are used
• Text file size


  (Bytes per character) x (Number of characters)
• Image file size


  (Resolution) x (Colour Depth)
• Sound file size


  (Sample Rate) x (Duration in seconds) x (Bit Depth)
• Hexadecimal


  Preferred in Computer Science when working with large values
• Where hexadecimal is used

  • MAC addresses
  • Colour values
• Binary shift


  How a computer system performs basic multiplication and division
• Left binary shift


  Multiplies a binary number by 2
• Right binary shift


  Divides a binary number by 2 (/2)
• Character set


  A defined list of characters that can be understood by a computer
• ASCII

  American Standard Code for Information Interchange, uses 7 bits to represent 128 characters
• Extended ASCII


  Uses 8 bits to represent 256 characters
• UNICODE


  Uses a minimum of 16 bits to represent 65,536 characters
• Bitmap image


  Made up of squares called pixels, each pixel stored as a binary code
• Vector image


  Created from mathematical equations and points, only the mathematics are stored
• Resolution

  The total amount of pixels that make up a bitmap image
• Colour depth

  The number of bits stored per pixel in a bitmap image
• As resolution and/or colour depth increases

  The file size becomes bigger
• Metadata


  Data about data, additional information stored with an image
• Types of Network

  • Local Area Networks (LANs)
  • Wide Area Networks (WANs)
• Analogue to Digital conversion (A2D)

  The process of converting an analogue sound wave into a digital form that can be stored and processed by a computer
• Local Area Network (LAN)


  • Small geographical area (under 1 mile)
  • Hardware is owned by the company/organisation/household using it
  • Uses unshielded twisted pair (UTP) cable, fibre optic cable or wireless connections (Wi-Fi)
• Sample rate


  The amount of samples taken per second of the analogue sound wave
• Wide Area Network (WAN)


  • Large geographical area (over 1 mile)
  • Collection of LANs joined together
  • Computers connected via routers
  • Hardware used to connect the networks is not all owned by the company/organisation/household using it
  • Uses fibre optic cable, telephone lines and satellite to connect the LANs together