Data representation (AQA GCSE COMPUTING)

what are the bases for decimal, binary and hexadecimal

decimal - base 10

binary - base 2

hexadecimal - base 16

why do computers use binary

to represent all data and instruction

what can bit pattern represent

text, images, sound and integer

what is a bit

a bit is the fundamental unit of information

what is a byte

a byte is a group of 8 bits

hwo can u represent a bit and a byte

b - bit

B - byte

true or false: a bit is either a 0 or 1

true

a kilo is how many bytes

1000 bytes

a mega is how many kilobyte

1000 kilobyte

a giga is how many megabytes

1000 megabyte

a tera is how many gigabytes

1000 gigabytes

0 + 0 = ?

0 + 1 = ?

1 + 0 = ?

1 + 1 = ?

1 + 1 + 1 = ?

0

1

1

write 0 then carry 1

write 1 then carry 1

where can binary shift be used

binary shift can be used to perform simple multiplication/division by powers of 2

what is a character set

a defined list of characters recognised by a computer, where every character is assigned a unique binary code

what number is letter A in ASCII

65

what number is letter a in ASCII

10

describe what character codes are

charcaters codes are grouped and they run in sequence eg: A = 65 and B = 66 etc….

what is the purpose of Unicode

to provide a globally recognized universal character set capable of representing all major world alphabets, mathematical symbols, and emojis

what are the advantages of using unicode rather than ASCII

different alphabets

special symbol allowing a far greater range of charcaters

true or False:Unicode doesn’t use the same codes as ASCII up to 127

FALSE:

Unicode uses the same codes as ASCII up to 217

what is pixel short for

picture element

define what a pixel is

a single point in an image

describe how pixels relate to an image and the way images are displayed.

Millions of these tiny coloured squares work together like a mosaic or a digital "paint-by-numbers" to form a complete picture

define image size

width x height

define colour depth

colour depth is the number of bits used to represent each pixel

How does a bitmap represent an image using pixels and colour depth?

A grid of individual dots called pixels are assigned a binary value determining it’s colour

Calculate bitmap image file sizes based on the number of pixels and colour depth.

Size = (bits) = W x H x D

Size = (bytes) = (W x H x D)/8

W = image width

H = image height

D = colour depth in bits.

what is sound and what must it be converted into for storage and processing

sound is analogue and that it must be converted to a digital from for storage and processing

define sample

sample is a measure of amplitude at a point in time

define sample rate and what it is measured in

Sampling rate is the number of samples taken in a second and is usually measured in hertz (1 hertz = 1 sample per second).

define sample resolution

Sample resolution is the number of bits per sample.

Calculate sound file sizes based on the sampling rate and the sample resolution.

File size (bits) = rate x res x secs

rate = sampling rate

res = sample resolution

secs = number of seconds

define what data compression

is the process of reducing the file size by re - encoding data using fewer bits

why may it be necessary or desirable to compress data

for maximum capacity and cost saving

how can data be compressed by using huffman coding

assigning shorter binary codes to frequently occuring characters and larger codes for rare ones

how to calculate the no. of bits required to be compressed by huffman coding

taking the no. of bits required char x no. of time the char appears in string

how to calculate the no. of bits required for uncompressed ASCII

count the total no. of char and multiply by 7 or 8 bits

How can data be compressed in RLE

replacin =g consecutive repeating char ( a run) with a single instance of a char and a count of it’s repetition

eg: AAAA BBB CCC —> 4A3B2C