Data representation

Data representation

1. Character set

   • Alphanumeric characters are used to make words and strings.
     • They include uppercase & lowercase letters, the digits 0-9, and symbols like ? + and £.
       • Character sets also contain special characters which do certain commands ( e.g. Space, enter & delete).
         • Pressing a button on your keyboard sends a binary signal to the computer and the computer uses the character set to translate the binary code into a character.
         • The number of bits you'll need is based on the character set.
           • ASCII is the most commonly used character set in the English-speaking world and has a 7 bit binary code, representing 128 different characters.
             • ASCII
               • Extended ASCII
                 • Unicode
                 • Tries to cover every possible character that might be written. It usually uses forms of 16-bit & 32-bit binary codes. It is good because it covers all major languages, even those that use an entirely different alphabet like Greek, Russian and Chinese.
                   • Image as binary
     • Computers are unable to process these characters directly as they only process binary code. So they need a way of converting characters to binary code and vice versa they can only do this using character sets.

2. The type of images you use most often are called bitmap images which are made up of tiny dots, called pixels.

   • The colour of each pixel is represented by a binary code. The number of colour available in and image is related to the amount of bits the code has.
     • Black and white images only use two colours meaning they only need 1-bit to represent each pixel (0 for white and 1 for black).
       • You can make a greater range of shades and colours by increasing the number of bits for each pixel.
         • Colour depth is the number of bits used for each pixel.
   • Most devices use a 24-bit colour depth, with 8 bits used to indicate the levels of red, green and blue needed for each pixel. It's estimated that the human eye can only see around 10 million different colours, meaning a 24-bit colour depth should be enough
     • Resolution is the density of pixels in an image measured in dpi (dots per inch).
       • The higher the resolution, the more pixels in a certain area and so the quality is better.
         • Increasing resolution or the colour depth means that there are more bits in the image which improves the quality but also increases the file size.
           • Sound as binary

3. Sound is sampled and stored digitally.

   • Sound is recorded by a microphone as an analogue signal which are pieces of continually changing data.
     • Analogue signals need to be changed into digital data in order for computers to be able to read and store sound files
       • The process of converting analogue to digital is called sampling
         • Sample rate - The number of times an analog signal is measured or sampled per second. Sample rate - The number of times an analog signal is measured or sampled per second.
         • Bit rate - The number of bits per second which can be transmitted along a digital network Bit rate = sample rate x bit depth.
           • Thousands of snapshots are taken of the sound. The more snapshots takes the higher the audio quality will be and the bigger the file size will be.
         • Binary

4. Binary only uses two different digits 0 and 1 we call this base 2.

   • To count in binary the place values from the right to the left (8, 4, 2, 1).
     • Binary conversions
       • • Each time you shift a binary number to the left you double the binary number. If you shift a binary number 3 places, you double it 3 times.
           • Each time you shift a binary number to the right you halve the binary number. If you shift a binary number 3 places, you have it 3 times.
           • Hex

5. Hex

   • Hex
     • Hexadecimal uses 16 different digits (base 16).
       • A single hex character can represent any denary number from 0-15. To represent 0-15 in binary would require 4 bits (a nibble), so each hex catheter equates to a nibble in binary.
         • Programmers often prefer hex when choosing because of the following: It's simpler to remember large numbers in hex - they're far shorter than binary numbers. Due to hex numbers being shorter, there's less chance of input errors. It's easier to convert between binary and hex than binary and denary.

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