Data Representation Flashcards
Why do computers use binary instead of decimal?
Less arithmetic rules need to be built into the computer
There is either a voltage or no voltage so a drop in voltage doesn’t affect the data being sent
The components inside a computer have only 2 states eg on/off, positive/negative, voltage/no voltage therefore the 2 symbols (1 and 0) used in binary are perfect
What 2 codes is text stored as?
ASCII or UNICODE
What is an advantage of UNICODE?
Can represent more characters, ASCII limited to 128 characters. so no problem storing characters of non Latin based languages such as Greek, Chinese etc.
Disadvantage of UNICODE?
Takes up more memory than ASCII as 16 bits (2 bytes) per character are used.
What are integers?
Integers are positive and negative whole numbers (ie NO DECIMAL POINT)
What method is used to store negative integers?
twos compliment
What is Floating Point Representation?
This is when the number is stored using 2 parts, the MANTISSA and the EXPONENT
What is the mantissa?
MANTISSA is a binary fraction between 0 & 1 and is normally stored using 4 bytes. The size of the mantissa affects the ACCURACY of the number.
What is the exponent?
The EXPONENT is the power and is normally stored using 1 byte. The size of the exponent affects the RANGE of the numbers available.
What 2 ways are graphics stored?
Bitmap or Vector Graphics
What is bitmap?
is when the image is stored as a series of pixels and each pixel is stored as a number of bits, depending on the number of colours used.
Advantage of bitmap?
Each pixel can be edited individually (perfect for air brushing of photos)
Disadvantage of bitmap?
Uses a lot of memory because every pixel including white spaces is saved
What is Vector Graphics?
Vector graphics is when each object is stored by its attributes.
e.g – A line may be stored by the following attributes :
( Line – start x, start y, end x, end y, line thickness, line colour, line pattern)
Advantages of Vector?
Takes up less memory than bit-mapped.
- Easy to resize, move and alter.
- Images are resolution independent i.e. same image quality regardless of resolution of display or printer.
- Quality of the image is not affected when enlarged.
- Objects can be grouped together and then manipulated as a single object.
Disadvantage of Vector?
Cannot be edited at pixel level.
- Limited to mathematical shapes
What is bit depth?
This is the number of bits per pixel and it affects the number of colours an image can display.
resolution?
This is the number of dot (pixels) per inch
What is true colour?
This is when an image had 24 bits per pixels. This means the image can display
16.8 million colours
What is an address bus?
This holds the address of where the next instruction has to be read from or written to. It is uni- directional i.e. only goes in one direction from processor to memory