2.1.4 Data Representation

2.1.4 Data Representation

1. Binary

   • Binary To Denary Conversion
     • Every normal number we deal with everyday there is a binary equivalent
       • Eg. The number 5 is 101
       • The conversion table looks like this...
   • Binary code is made up of only 0s and 1s because its base 2
   • Computers read everything in binary. Every letter, symbol or number.
   • Binary addition is simple...
     • You simply take your numbers and add them using these rules...
       • 1+1=0 but you carry the one to the next column
       • 1+0 or 0+1 = 1 with no carried numbers
       • 0+0 = 0

2. Hexadecimal

   • Hexadecimal (or hex) is a number system which uses base 16
   • As we only have 10 digits, it uses 0-9 and then letters A to F
     • Less likely to make an error with fewer characters
   • Much simpler to remember a hex value than a binary value
   • Quicker to write or type since a hex digit only takes up 1 character, not 4
     • Easy to convert to and from binary

3. Images

   • The main image types are...
     • JPEG or JPG
     • Bitmap or BMP
     • GIF
     • PNG
     • TIF
   • Pixels
     • A pixel is the smallest identifiable area of an image
     • Each pixel is a single colour and is given a binary value which represents that colour e.g. 11000000 might equal Red
     • A pixel’s colour can be changed by changing this value
   • Resolution
     • Resolution is the concentration of pixels within a specific area
     • The area is defined by the image width and height in pixels e.g. 3264x2448
     • 72dpi = screen resolution
     • 300 dpi = print quality resolution
     • The higher the resolution the better the image looks but the file size becomes a lot bigger
   • Creating Images
     • 1. Each Pixel is given a binary value
     • 2. Each value represents a different colour
     • 3. Using one bit per pixel allows only 2 values, 0 and 1
     • Eg. 1=Black White=0

4. Sound

   • Sampling
     • Recording quality improves: the more frequently we sample the sound and the more accurately we record the wave height
     • Increasing sampling rate and resolution means recording more data points
     • Sound sampling is turning this --->
       • To this --->
   • Lossy Compression
     • Lossy compression removes the sounds in the frequency ranges that we can’t so easily hear or that least affect the perceived playback quality
     • Lossy compression leaves out some data – this can affect the sound quality
   • Analogue and Digital Sounds
     • Analogue sounds are continuous and digital sounds are discrete
     • Sound is digitized by repeatedly measuring and recording the sound wave
   • Lossless Compression
     • Lossless compression leaves out repeated data and instead makes a note of how many times it is repeated
   • File Formats
     • .WAV – uncompressed files
     • .FLAC or .M4A lossless compression, slightly smaller files
     • .MP3 – Lossy compression, much smaller files

5. Machine Code

   • Machine code is the ONLY language computers can understand
     • An instruction code is written in the form 0101 01 01001101
       • Its made up of 0s and 1s
     • Operands
       • The operands are the data or memory location actually used in the operation
     • OP Codes
       • The 1st four binary digits are the 'op code'. Op codes are operations the computer has been coded to do automatically
       • Eg. the code 0101 could make the computer copy a register to a memory location.
     • Register
       • All computers have registers. They are a volatile area to store data
       • Computers have different amounts of registers. If the register number is two digits long, the computer has 4 registers.

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