COS1521 DATA TYPES

COS1521 DATA TYPES

1. DATA TYPES

   • Numbers
   • Text
   • Audio
   • Images
   • Video

2. Bit Pattern

   • Used to represent different types of data. A piece of data belonging to different data types can be stored as the same pattern in memory
   • A pattern with 8 bits is called a byte

3. NB! All kinds of data are stored in the form of bit patterns. All data in memory is in binary form, even if hexidecimal is used to display memory contents on the screen.

4. STORING NUMBERS

   • UNSIGNED
     • Can never be negative: 0 to (2 ** n - 1 ) where n is the number of bits allocated.
     • OVERFLOW
       • Overflow will occur if the number of bits required to store the data exceeds to number of bits allocated.
   • SIGN-AND-MAGNITUDE
     • 0 to (2 ** n - 1) is the number of bits allocated
     • Split into 2 halves, 1st half positive (0000 to 0111), 2nd half negative (1000 to 1111)
     • Has 2 zeroes: + 0 (0000) and - 0 (1000)
     • Leftmost bit determines the sign of the integer. 0 = positive and 1 = negative
     • Range of either half (2 ** (n-1) - 1)
     • NEGATIVE AND POSITIVE OVERFLOW
   • TWO'S COMPLEMENT
     • bit allocation 0 to (2 ** n -1)
     • STORING
       • Integer is changed to n-bit binary
       • If integer is positive or zero, stored as is. If the integer is negative, two's complement is taken and it is then stored
     • RETRIEVING
       • If leftmost bit is 1, two's complement operation, if 0 no operation
       • Changed to decimal
     • NEGATIVE AND POSITIVE OVERFLOW
   • An integer is normally stored in memory using fixed-point representation

5. STORING REALS

   • INCOMPLETE

6. STORING TEXT

   • Each character/symbol has a bit pattern associated with it. So a four letter word requires four different bit patterns.
   • ASCII
     • Today it is part of Unicode
   • Unicode
     • Uses 32 bits and therefore can have 2 ** 32 different characters/symbols

7. STORING VIDEO

   • Video is a representation of images (frames) that are relayed over time.

8. STORING AUDIO

   • Audio is an example of analog data
   • Sampling is done to take a certain number of samples over a period of time and record them (sampling rate).
   • The value measured for each sample is a real number. Quantization is done to round each value to the closest integer value
   • Values are then Encoded into bit patterns
   • The number of bits assigned to a sample is known as bit depth
   • Bit rate is the product of the sampling rate and the bit depth

9. STORING IMAGES

   • RASTER GRAPHICS
     • used to store an analog image
     • Samples are taken called pixels
     • Resolution is the number of pixels per square or linear inch
     • Color depth is the number of bits used to represent a pixel
       • TRUE COLOR
         • Uses 24 bits to encode a pixel. Using RGB made up of 3 X 8-bit patterns
       • INDEXED COLOR
         • Uses a portion of colors from the True Color scheme usually 256 ( 0 to 255 )
     • File size is big and rescaling is troublesome
   • VECTOR GRAPHICS
     • Does not store each pixel as a bit pattern
     • Each image is composed of a combination of geometrical shapes
     • Each shape is represented by a mathematical formula
     • A Set of commands that define how the object is to be drawn essentially