Chapter 4 - Representing Data
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In binary what does 1 + 0 = 1 + 1 = 0 + 0 = 1 + 1 + 1 =
1 + 0 = write 0 carry 1 over 1 + 1 = write 0 carry 1 over 0 + 0 = write 0 1 + 1 + 1 = write 1 carry 1 over
What is an overflow error?
When the result of an addition is too big to fit in the available space Eg. When a computer uses storage values that are 8 bit long, by adding two 8 bits long numbers, the result may be bigger than 256 - you need a 9th binary digit, the 9th digit will be lost
Count to 15 in hexadecimal
0 1 2 3 4 5 6 7 8 9 A B C D E F
Why use hexadecimal numbers?
Large binary numbers are hard to remember and programmers want something that is easily converted from binary an easy to remember and recognise
How are images stored?
Images are stored as a series of binary values, each binary value is one pixel
What is metadata and why is there a need for it?
Metadata is data about data It includes height and width, resolution, but depth etc There is a new for metadata because it enables the computer to work out how to turn these binary values into an image
What is height and width measured in?
Pixels
What is couloir depth?
The number of bits used per pixel, or how many colours each pixel can represent 1 bit = 2 colours black or white 2 bits = 2*2 colours or 4 colours Etc. The more bits per pixel the greater the colour depth
What is resolution?
Number of pixels per unit eg number of pixels per inch or dpi (dots per inch)
The higher the colour depth and the higher resolution, what happens to the size of an image file?
It increases
When does an image become pixelated?
When a bitmapped image is enlarged
What are the units of storage?
Bit Nibble Byte Kilobyte Megabyte Gigabyte Terabyte
How are characters steed?
All characters and symbols are represented by a code The codes used are stored in binary The computer looks up the symbol matching the code from a list of codes and their associated character
What is a character set?
The list of codes and matching characters is called a character set
What determines how many symbols are in a character set?
The number of bits used to store each symbol
Examples of character sets?
Unicode ASCII
How many bits does ASCII use?
8 bits per character = 256 possibilities
How many bits does uni code use?
16 bit providing 65 000 possibilities Or 32 bits = 4 billion possibilities
Why is unicode better than ascii?
Because it provides a wider range of characters and symbols facilitating communication
What is sound and how is in stored in digital form?
Sound is analogue (continuously varying) so to transfer sound to a computer it must be digitally sampled.
What is sample rate?
The number of samples in a second
What is sample interval?
The time between samples been taken
The higher the sample interval…
The lower the sample rate
When a sound is sampled at a low rate:
Very few samples are taken There is poor match between the original sound and the samples sound A small file size is required