3 - Data representation

Question 1

Why is hexadecimal often used in computer science?

Answer 1

-easier for people to read/remember (shorter representation)
-faster to convert to/from binary

Question 2

Why can’t you use hexadecimal to save storage space on a computer?

Answer 2

computers only read/understand binary, so it will be stored as binary and not hex

Question 3

What are binary shifts?

Answer 3

multiplying/dividing a binary number by a power of 2 by shifting all the digits up/down

Question 4

What is a character set?

Answer 4

all the symbols that can be understood and displayed by a computer

Question 5

What does ASCII stand for?

Answer 5

American Standard Code for Information Interchange

Question 6

How many bits does ASCII use, and how many characters can be represented using this many?

Answer 6

7

(2⁷=) 128

Question 7

Why is Unicode often used over ASCII?

Answer 7

more characters can be represented

uses 16 bits usually but you don’t need to know that

Question 8

How is Unicode similar to ASCII?

Answer 8

the first 127 characters of Unicode are all of the ASCII characters

Question 9

What is colour depth?

Answer 9

number of bits used to represent the colour of each pixel

Question 10

What is a pixel, and what is it short for?

Answer 10

-smallest addressable point in an image

-picture element

Question 11

What is a bitmap?

Answer 11

an array of pixels used to make an image

Question 12

How is analogue sound recorded so that it can be stored on a computer?

Answer 12

analogue sound signals are sampled at regular intervals as a series of bits to convert it to digital

Question 13

What is a sample, and what is sampling rate?

Answer 13

-a measure of the amplitude of a sound at a point in time

-sampling rate is the number of samples recorded in a given time

Question 14

Give an advantage of using a higher sampling rate:

Answer 14

the resulting digital sound is a closer representation of the analogue sound

Question 15

Define sampling resolution:

Answer 15

number of bits per sample of audio

Question 16

What are the 2 types of compression?

Answer 16

-lossless (no reduction in quality, can be used on text)
-lossy (original data cannot be reconstructed)

Question 17

What does Huffman encoding do to data?

Answer 17

takes most frequently used data and assigns it a bit pattern with the least number of bits

A form of lossless compression

Question 18

How do you construct a Huffman tree?

Answer 18

-create a frequency table of all the characters used (including spaces)
-write them in a line in order of frequency
-pair up adjacent letters with the smallest frequency, and add their frequencies up to get another value to put above
-repeat the pairing process until you get 1 value at the top (total number of digits)

-assign left/right to be 0/1, find bit pattern for each letter

Question 19

How does run length encoding (RLE) compress data?

Answer 19

-takes a string of bits
-stores it in frequency-data pairs (eg 4x1s means 1111)

Not necessarily in that format of 4x1s

RLE can sometimes increase the file size if there aren’t many bits in the first place

Question 20

Why is data compressed?

Answer 20

-to reduce its file size so it decreases the amount of storage it takes up
-to make it faster to transmit as it takes up less bandwidth