1.2 Storage and compression

Question 1

RAM

Answer 1

Random access memory
Volatile
Very fast
Read/ write
Holds data and instructions currently in use- for example:
* current volume, video, channel, browser, OS

Question 2

ROM

Answer 2

Read only memory
Holds BIOS
Located on motherboard
Slower than RAM
Non-volatile

Question 3

RAM vs ROM

Answer 3

RAM volatile, ROM non-volatile.
RAM is read/write, ROM is read-onnly

Question 4

Virtual memory

Answer 4

RAM almost or completely full
Data not currently being executed sent to a small portion of seconday storage allocated for virtual memory
RAM is filled with data which needs to be executed
Data is transferred back as needed

Slow

Question 5

Need for secondary storage

Answer 5

Long term storage of programs and data that are currently not in use

Question 6

Storage devices

Answer 6

Magnetic

Solid State

Optical

Question 7

Magnetic

Answer 7

Capacity - High storage
Cost - Low per gigabyte
Speed - Moderate read/write access

Durability - Moving parts can get damaged if dropped
Portability - Heavy & bulky making them less convenient for transport
Reliability - Prone to mechanical failure
Noise - Loud (spinning disks)

Question 8

Solid State

Answer 8

Durability - No moving parts
Portability - Small and no moving parts
Noise - Silent
Capacity - Medium/high storage
Speed - Very fast read/write access

Cost - Very high per gigabyte
Reliability - Limited read/write cycles

Question 9

Optical

Answer 9

Cost - Very low per gigabyte
Durability - No moving parts
Portability - Small and no moving parts
Noise - Silent

Reliability - Prone to scratches
Speed - Very slow read/write access
Capacity - Very low

Question 10

Hard Disk Drive

Answer 10

Magnetic

500GB - 8TB (consumer-grade)

Low cost per GB

Question 11

SSD

Answer 11

Solid-State Drive (SSD)

Solid Stae

128GB - 2TB (consumer-grade)

High cost per GB

Question 12

USB Flash drive

Answer 12

Solid State

8GB - 256GB (common sizes)

Moderate cost per GB

Question 13

CD/ DVD/ Blu-Ray

Answer 13

Optical

CD: 700MB, DVD: 4.7GB - 9GB, Blu-ray: 25GB - 50GB

Low cost per disc

Question 14

What is a character set

Answer 14

All of the characters which can be understood by a computer

Question 15

ASCII

Answer 15

7 bit = 128 possible characters

Question 16

Extended ASCII

Answer 16

8 bit = 256 possible characters

Question 17

ASCII/ extended ASCII limitations

Answer 17

ASCII cannot represent characters from languages other than English

ASCII does not include modern symbols or emojis common in today’s digital communication

Question 18

UNICODE

Answer 18

128 bits = 65,536 possible characters
It can represent more characters than ASCII.
It can support all common characters across the world.
It can represent special characters such as emoji’s.
Uses a lot more storage than ASCII

Question 19

BItmap

Answer 19

A bitmap image is made up of squares called pixels
A pixel is the smallest element of a bitmap image
Each pixel is stored as a binary code
Binary codes are unique to the colour in each pixel
A typical example of a bitmap image is a photograph

Question 20

Vectors

Answer 20

A vector image is created from mathematical equations and points
Only the mathematics used to create the image are stored
For example, to create a circle the data stored would be:
Centre point (x, y coordinates)
Radius
Typical examples of vector images are logos and clipart

Question 21

Resolution

Answer 21

Resolution is the total amount of pixels that make up a bitmap image
The resolution is calculated by multiplying the height and width of the image (in pixels)
In general, the higher the resolution the more detail in the image (higher quality)
Resolution can also refer to the total amount of pixels horizontally in a display, such as:

Question 22

Color depth

Answer 22

Colour depth is the number of bits stored per pixel in a bitmap image
The colour depth is dependent on the number of colours needed in the image
In general, the higher the colour depth the more detail in the image (higher quality)
In a black & white image the colour depth would be 1, meaning 1 bit is enough to create a unique binary code for each colour in the image (1=white, 0=black)

Question 23

Impact of higher color depth / resolution

Answer 23

As the resolution and/or colour depth increases, the bigger the size of the file becomes on secondary storage
The higher the resolution, the more pixels are in the image, the more bits are stored
The higher the colour depth, the more bits per pixel are stored

Question 24

Metadata

Answer 24

Data about data
* Author - Who created the image?
* Date/Time - When and what time was the image created/taken?
* Location - Where was the image taken?
* Width & height of the image (resolution)
* Colour depth

Question 25

How is sound stored

Answer 25

Sound is analogue but needds to be digital (A2D conversion) The amplitude of a sound wave is measured at set intervals every second (sample rate in Hz)

Question 26

CD sample rate

Answer 26

44.1kHz

Question 27

What is compression

Answer 27

Compression is reducing the the size of a file so that it takes up less space on secondary storage MInimises file transfer time

Question 28

Lossy compression

Answer 28

Lossy compression is when data is lost in order to reduce the size on secondary storage Lossy compression is irreversible Lossy can greatly reduce the size of a file but at the expense of losing quality Lossy is only suitable for data where reducing quality is acceptable, for example images, video and sound In photographs, lossy compression will try to group similar colours together, reducing the amount of colours in the image without compromising the overall quality of the image

Question 29

Lossless compression

Answer 29

Lossless compression is when data is encoded in order to reduce the size on secondary storage Lossless compression is reversible, the file can be returned to its original state Lossless can reduce the size of a file but not as dramatically as lossy Lossless can be used on all data but is more suitable for data where a loss in quality is unacceptable, for example documents In a document, lossless compression uses algorithms to analyse the contents looking for patterns and repetition. For example, repeating characters are replaced with a single character and the number of occurrences in the document (“EEEEE” becomes “E5”)