Memory and storage Part 2

Question 1

What is binary?

Answer 1

Binary is a number system consisting of only 0s and 1s

Question 2

Why must data be stored in a binary format?

Answer 2

Computers consist of billions of transistors, which are switches, that only contain two values - on and off. Therefore all data must be represented and processed this way.
Everything that a computer needs to process must be converted into binary format, including text, images, video and audio.

Question 3

What are the different units of data storage and how many bytes are in each one?

Answer 3

1 bit = a single 0 or 1
1 nibble = 4 bits
1 byte = 8 bits = 1 character of text
1KB (kilobyte) = 1000 bytes
1MB (megabyte) = 1000 kilobytes
1GB (gigabyte) = 1000 gigabytes
1TB (terabyte) = 1000 gigabytes
1PB (petabyte) = 1000 terabytes

Question 4

How many possible combinations or states can 5 switches produce?

Answer 4

32 (basically 2 to the power of that number, as binary is a base 2 system)

Question 5

What is the most significant bit? (MSB)

Answer 5

The bit with the largest value (furthest to the left)

Question 6

What is the least significant bit? (LSB)

Answer 6

The bit with the smallest value (furthest to the right)

Question 7

What is 28 in binary using 8 bit binary?

Answer 7

00011100

Question 8

What is 1010111 in denary?

Answer 8

87

Question 9

What are the 16 times tables (up to16*16)

Answer 9

16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256

Question 10

What are the powers of 2 (up to 2^20)

Answer 10

2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16348 32768 65536 1310722 262144 524288 1048576

Question 11

Convert BB from hex to denary

Answer 11

187

Question 12

Convert 106 from denary to hex

Answer 12

6A

Question 13

Convert 83 from hex to binary

Answer 13

10000011

Question 14

Convert 00111110 from binary to hex

Answer 14

3E

Question 15

Why do programmers use hex?

Answer 15

It is simpler to remember a hex value than a binary value
It is quicker to write or type
People are less likely to make an error with fewer digits
It is easy to convert between hex and denary
NB: never refer to computers when answer this question, as they only understand binary! Hex is purely for the people!

Question 16

What is overflow error?

Answer 16

When the result of an addition is too large for the number of bits the computer works with, there will be an overflow error

Question 17

What does a binary shift left of one bit do?

Answer 17

it moves all the bits one place to the left, with the vacant bit spaces filling up with zeros, and DOUBLES the number

Question 18

What does a binary shift right of 2 places result in?

Answer 18

It halves the number and rounds down each time, essentially dividing by 4 (2^2)

Question 19

What are the effects of logical shifts?

Answer 19

Logical shifts can very quickly multiply or divide a binary number by a factor of two
A loss of accuracy can occur if 1 bits are removed

Question 20

Around how many unique characters are available on a keyboard, and therefore how many bits should be used?

Answer 20

There are around 98 unique characters, therefore 7 bit binary should be used to represent them

Question 21

What is a character set and how is it ordered?

Answer 21

A character set is a set of letters, numbers, symbols and digits that can be represented by a computer.
Character sets are ordered logically, so the code for ‘B’ will be one greater than the code for ‘A’.

Question 22

What are the two major character sets in use today?

Answer 22

ASCII and Unicode

Question 23

What is ASCII and what are its characteristics? (Think exam for bits)

Answer 23

ASCII is the standard code, used worldwide and uses 7-bit binary codes. Extended ASCII uses 8-bit binary, and that’s what’s going to be used in the exam, so 256 different characters can be encoded.
Characters include numbers 0-9, uppercase and lowercase, letters A-Z, a-z, punctuation symbols and the space character
Originally developed for representing the English alphabet

Question 24

How are character codes grouped on ASCII?

Answer 24

Character codes are commonly grouped and run in sequence. Numeric characters 0-9 run consecutively from 48-57 on the ASCII table. A-Z characters are from 65-90 or 01000001 to 01011010. a-z characters use 97-122

Question 25

True or false: the ASCII character code that represents the character '7' is the same as binary code that represents the integer 7 in programming.

Answer 25

FALSE! 55(0110111) is the ASCII character code that represents the character '7'. In programming, this is very different to the integer 7 which is represented by 00000111 (7)

Question 26

Can you do arithmetic with characters?

Answer 26

No - if a character represents a number it must first be converted to an integer before any arithmetic is carried out.

Question 27

What is the other commonly used character set and why is it used?

Answer 27

Unicode is the other commonly used character set, and it is used to represent other characters for different languages, as more characters are needed. Unicode uses 16 bits - so 65,5356 possible combinations. Unicode is also used to store emoji

Question 28

What is the denary, hex, and binary number range?

Answer 28

Denary: 0-255 Hex: 00-FF Binary: 00000000 - 11111111

Question 29

Kate's solid state drive on the tablet has 40GB of space. The camera on the tablet produces images of size 200,000 KB. How many images can she store on the drive? Show all working.

Answer 29

200 images

Question 30

True or false: different storage devices have different FIXED capacities

Answer 30

TRUE

Question 31

Order the capacity of these different files (nothing is in order): 1 character of text; 1 byte DVD capacity; 30kB One small digital colour photograph; 3MB A full page of text; 650MB Music CD Capacity; 4.5GB Hard Disk Capacity; 1TB

Answer 31

1 character of text - 1 byte A full page of text - 30kB One small digital colour photograph - 3MB Music CD Capacity - 650MB DVD Capacity - 4.5GB Hard Disk Capacity - 1TB

Question 32

What is data capacity?

Answer 32

Data capacity is the maximum amount of information that a storage device can hold.

Question 33

Lyla is a social media influencer. She creates images to be shared on her social media accounts. Each image has a fixed size of 3 MB. She is storing the images on a USB flash drive which has a capacity of 6 GB. Calculate how many images can be saved on the storage device. Show your working [2]

Answer 33

How to answer this question: Convert 6 GB to MB Divide the capacity in MB by the files size in MB Answer 6 GB = 6 * 1000 = 6000 MB 6000 / 3 = 2000 images

Question 34

What is a bitmap graphic?

Answer 34

A bitmap graphic is a digital image, which is divided into a grid of picture elements called pixels. When pixels of an image are mapped to binary codes for their colours, a bitmap is created.

Question 35

What is a pixel?

Answer 35

A pixel is the smallest addressable part of an image. It can only have one colour at a time, but it is addressable, meaning that the colour can be changed.

Question 36

What is colour depth?

Answer 36

Colour depth is the number of bits used to represent a colour value of a single pixel in an image. E.g. black and white images (monochrome) allocate 1 bit to each pixel allowing two colours (1 for black and 0 for white) 2^1 2^n = colours; n = no. of bits per pixel

Question 37

What is image resolution?

Answer 37

Image resolution is expressed as the number of pixels in an image.

Question 38

How do you calculate the memory required for bitmaps?

Answer 38

Memory required = total no. of pixels x no. bits per pixel from colour depth

Question 39

How do you calculate text file size?

Answer 39

text file size = bits per character x no. of characters

Question 40

What is metadata? How is it stored?

Answer 40

Metadata is a set of standardised information about a picture, meaning data about data. It is stored as part of the file. DATA ABOUT DATA

Question 41

What are examples of metadata?

Answer 41

Width of picture Height of picture Resolution of picture Colour depth Location of picture Any type of camera setting (e.g. lens) Metadata is only talking about pictures - so make sure to give examples that are relevant to pictures only, not just any file

Question 42

What are the characteristics of lossless compression?

Answer 42

No information is lost File can be returned to original condition Stores information in reduced form which can be used to recreate file e.g long runs of same colour pixels (run length encoding)

Question 43

What are the characteristics of lossy compression?

Answer 43

Discards information which is considered less important or can't be noticed by human eye e.g background File cannot be reutrned to original condition More suitable for photographs with every changing pixel colours

Question 44

What are the advantages of using lossy compression over lossless and vice versa?

Question 45

What file types are lossy and what are lossless?

Answer 45

Lossy compression: JPEG - used for photos Lossless compression: Gif - simple logos only or animated gifs (sequences of images) png - as with gif, but 24 bit not 8 bit Tiff - high quality, used for printing Bmp - original, uncompressed image - editing Psd - photoshop file - retains layers for editing

Question 46

What is sound?

Answer 46

Sound is a vibration of the air (in waves) causes eardrum to move brain senses movement as sound

Question 47

What is frequency?

Answer 47

Frequency is the number of times sound waves vibrate per second - measured in no. of cycles per second (Hz) Frequency is pitch amplitude of wave is loudness

Question 48

How is sound recorded?

Answer 48

Micophone (transducer) converts sound waves to electrical voltage signals Resulting signal is an analogue (or continuous) signal Computers are digital so need to convert this analoque signal to a digital signal (binary) for a computer to process Sound is then sampled (converting analogue sound signal into a digital file containing binary numbers done by ADC

Question 49

What is sampling?

Answer 49

Sampling involves measuring the amplitude of a wave at regular intervals. These are then quantised (rounded) into one set number of values and stored together in a binary file.

Question 50

How can you improve the accuracy of a sample?

Answer 50

By taking samples at more frequent intervals, the digital signal will come closer to approximating the analogue signal.

Question 51

What is sampling rate?

Answer 51

Sampling rate is the number of times sound is sampled per second. Measured in Hz

Question 52

What is sampling depth (accuracy/bit depth)?

Answer 52

Sampling depth is the number of bits per sample (like the sound version of colour depth)

Question 53

What is bit rate?

Answer 53

bit rate is the space available for each sample. Measured in kilobits/sec

Question 54

How do you calculate the size of a sound file?

Answer 54

size = bit rate x time (like speed x time) bit rate = sampling rate x no. bits per sample so size = sampling rate x sampling depth x time

Question 55

What are the factors affecting sound quality?

Answer 55

Sampling frequency (no. samples per second) Sampling accuracy (no. bits per sample) Bit rate amount of storage - file size

Question 56

What are the different ways of storing sound in files and where are they used?

Answer 56

WAVE (.WAV) - pure uncompressed sound high quality large file size - approx. 2.5MB storage for 1 min used for CDs MPEG compressed sound - removes frequencies ear will not miss or brain cannot process much lower quality file size 10 times smaller - 0.25MB for 1 min approx used on internet/downloads

Question 57

Why are character sets needed?

Answer 57

Character sets are necessary because they allow computers to exchange data and humans to input numbers.

Question 58

How is an image represented on a computer?

Answer 58

An image is a series of pixels represented in binary. Each pixel has a specific colour, represented by a specific code.

Question 59

How does increasing the colour depth affect the image?

Answer 59

Increasing the colour depth increases the quality of the image and the file size of the image.

Question 60

How does increasing the resolution affect the quality and size of an image?

Answer 60

Increasing the resolution of the image increases the quality and file size of the image.

Question 61

What is the effect of bit depth on the playback quality and size of a sound file?

Answer 61

The higher the bit depth, the more accurately a sound can be recorded as more bits are available to use for each sample, but the larger the file size. So, increasing the bit depth increases the playback quality and the size of the sound file.

Question 62

What is the effect of the duration of a sound file?

Answer 62

Duration is how many seconds of audio the sound file contains. So, increasing the duration of a sound file increases the size of the sound file.

Question 63

What is sample rate measured in?

Answer 63

Hz

Question 64

What is the effect of sample rate on the playback quality and size of a sound file?

Answer 64

The higher the sample rate, the better the playback quality as the digital data more closely represents an analogue wave. However, higher sample rates result in larger file sizes because more data is stored for each individual.

Question 65

Why is compression needed?

Answer 65

Modern computers often generate files of very large sizes. For example, audio files often run to megabytes, while high definition video can be gigabytes in size. Such files require lots of storage space, and, because of their size, are difficult to transmit. These problems can be overcome by using compression. .