1.2- Memory and Storage

Question 1

What is primary storage?

Answer 1

“Main Memory”- RAM and ROM
Contain all the data and instructions the computer is currently using
Much faster than secondary storage.

Question 2

What is RAM?

Answer 2

Volatile, read-write memory that holds data and instructions the computer is currently using

Question 3

What is ROM?

Answer 3

Non-volatile, read only memory that holds boot up and basic instructions (eg BIOS). Can be updated by flashing. Normally fixed to motherboard.

Question 4

How does ROM boot up a computer?

Answer 4

Instructions in ROM first check hardware and ensure everything is working (POST). ROM finds operating system on secondary storage, copies to RAM and puts OS in charge.

Question 5

What is virtual memory?

Answer 5

When RAM is filled, computer allocates space on secondary storage to act as RAM. Oldest RAM applications are moved to virtual memory and then swapped back when they are used again.

Question 6

Negatives of Virtual Memory

Answer 6

Needs to copy back into RAM to be read
If happens regularly can slow system dramatically

Question 7

What is secondary storage?

Answer 7

Used as long term storage.
Contains OS, programs, documents and data.
Non volatile, so retains data while computer is off.

Question 8

What are 3 types of secondary storage?

Answer 8

Optical: CD (<720MB), DVD (<8.4GB), Blu-Ray (<50GB). Uses lasers to read and write data while disc spins.
Very cheap, quite durable and very portable. Low capacity, easily scratched and low speeds.

Magnetic: HDD, magnetic tape (long term backup), floppy disk. Magnets charge particles to represent bits.
Very high capacity, good value. If bumped could be damaged, noisy and use more energy than SSD.

Solid State: Non-volatile RAM to store data when power is off. Normally much faster. No moving parts, more durable and use less energy. More expensive per GB and have limited number of write attempts.

Question 9

How many bits in a nibble?

Answer 9

4 bits

Question 10

How many bits in a byte?

Answer 10

8 bits

Question 11

How many bytes in a kilobyte?

Answer 11

1000 bytes

Question 12

How many kilobytes in a megabyte?

Answer 12

1000 kilobytes (1 million bytes)

Question 13

How many megabytes in a gigabyte?

Answer 13

1000 megabytes

Question 14

How many gigabytes in a terabyte?

Answer 14

1000 gigabytes

Question 15

How many terabytes in a petabyte

Answer 15

1000 terabytes

Question 16

Sound File Size =

Answer 16

Sample rate x duration (s) x bit depth

Question 17

Image File Size =

Answer 17

Colour depth x image height (px) x image height (px)

Question 18

Text File Size =

Answer 18

Bits per character x number of characters

Question 19

What do binary shifts do?

Answer 19

Multiplies and divides binary numbers
x2 = shift left once
x4 = shift left twice
etc

Question 20

What is an overflow error?

Answer 20

When there isn’t enough room for a result

Question 21

Binary addition rules

Answer 21

0+1=1
1+1=0 carry 1
1+1+1=1 carry 1

Question 22

What is a character set?

Answer 22

Where each letter/symbol utilised by the set is assigned a binary code so the computer can represent characters.

Question 23

Name 3 character sets

Answer 23

ASCII
Extended ASCII
Unicode

Question 24

How does number of bits per character affect total number of characters in a character set?

Answer 24

The more bits per character, the more characters can be used in the set as there are more options.
Eg. 7 Bit = 128 possible characters, 8 bit = 256 possible characters

Question 25

How are images represented?

Answer 25

A series of pixels that each have a specific colour, which is assigned a specific binary code

Question 26

How does colour depth affect quality and size of image?

Answer 26

Greater colour depth= Greater quality as more colours can be represented, greater image size

Question 27

What is resolution

Answer 27

Number of pixels image contains. Greater resolution = greater quality, greater file size

Question 28

What is sampling?

Answer 28

Taking measurements of the amplitude of the sound wave at regular intervals. This value assigned binary value in order to digitise an analogue sound wave.

Question 29

What is sampling rate?

Answer 29

How many samples are taken per second - measured in Hz.

Question 30

How does sampling rate affect sound?

Answer 30

Greater sampling rate = closer digital representation to actual sound

Question 31

What is sampling size?

Answer 31

Amount of storage space allocated to storing each sample.
Sample size of 8 bits allows 256 different values.

Question 32

What is bit rate?

Answer 32

Amount of storage required to store 1 second of sound.
Sampling frequency x Sample size

Question 33

How does sample rate, bit depth and duration affect playback quality and file size?

Answer 33

Greater sample rate/ bit depth/ duration = greater file size
Greater sample rate/ bit depth = better playback quality

Question 34

What is metadata?

Answer 34

Data about data.
Includes data about the file itself, such as file type, date created, author.
In images, includes resolution, colour depth, height x width of image.

Question 35

What is lossy compression?

Answer 35

Lossy compression removes some of the file’s original data in order to reduce file size.
Eg. JPEG, MP3

Question 36

What is lossless compression?

Answer 36

Reduces file size without removing any original data from file. Used when it is vital that the file can be restored to its original form.
Eg. ZIP