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computer science > 1.2 Memory and Storage > Flashcards

1.2 Memory and Storage Flashcards

1
Q

Why do computers need primary memory?

A

The read and write speed on a hard disk is very slow compared to Main Memory yet the cost of faster speeds means that Main Memory doesn’t have enough storage space

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2
Q

Features of RAM

A
  • Random Access Memory
  • Stores part of the OS and software in use
  • Can be read from and written to
  • Volatile
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3
Q

Features of ROM

A
  • Read Only Memory
  • Stores start-up programs, various firmware for the control of the components, bootstrap which tells the computer where to find the OS on the hard drive and Basic Input/Output System (BIOS) which controls the configuration of components
  • Can only be read from
  • Non-volatile
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4
Q

When is virtual memory needed?

A

When there isn’t enough physical RAM space to store open programs

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5
Q

Where is virtual memory stored?

A

On the hard disk

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6
Q

How does virtual memory work?

A
  • Programs are transferred out to virtual memory from the RAM when they aren’t currently being executed
  • Programs are transferred back to RAM when they’re needed
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7
Q

Optical storage

A

Lasers read and write data using light

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8
Q

Magnetic storage

A

Mechanical parts e.g. a driver head move over the disk to read and write data magnetically

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9
Q

Features of optical storage (Capacity, Speed, Portability, Durability, Reliability, Cost)

A
  • Bad compared to others
  • Bad, accessed in a spiral
  • Good
  • Bad, prone to scratches
  • Medium, can become damaged easily
  • Good, cheap to buy in bulk
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10
Q

Features of magnetic storage (Capacity, Speed, Portability, Durability, Reliability, Cost)

A
  • Good
  • Medium, can only be read sequentially
  • Medium, moving when powered on can damage the device
  • Medium, moving parts eventually fail
  • Medium, can become damaged or moving parts can fail
  • Good, cheaper cost per gigabyte than solid state
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11
Q

What are the features of virtual memory?

A
  • Cheaper than increased RAM
  • Prevents error message ‘out of memory’ while programs and files remain open
  • Takes more time to access than data stored in RAM due to transfer time
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12
Q

Features of solid state storage (Capacity, Speed, Portability, Durability, Reliability, Cost)

A
  • Medium
  • Good, data doesn’t need to be accessed sequentially
  • Bad, limited number of read/write cycles
  • Good, no moving parts
  • Medium, price is decreasing as technology improves
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13
Q

Nibble

A

4 bits

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14
Q

Byte

A

8 bits

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15
Q

What is the order of units of data?

A

kB, MB, GB, TB, PB

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16
Q

0+0

A

0

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17
Q

1+0

A

1

18
Q

1+1

A

0 carry 1

19
Q

1+1+1

A

1 carry 1

20
Q

Shift left

A

Multiply by 2

21
Q

Shift right

A

Divide by 2 (empty positions are filled with 0s resulting in a loss of accuracy)

22
Q

Most significant bit

A

Largest power of 2

23
Q

Least significant bit

A

Smallest power of 2

24
Q

Binary to hex and vice versa

A

Each nibble converted separately e.g. 11011001=D9

25
Q

Denary to hex and vice versa

A

Divide by 16 for first digit value, remainder is second digit value e.g. 217=D9

26
Q

Character set

A

A logically ordered set of all characters that can be encoded using a given number of bits

27
Q

American Standard Code for Information Interchange

A

7 bits (128 characters)

28
Q

Extended ASCII

A

8 bits (256 characters)

29
Q

Unicode

A

16 bits (63,536 characters) used for all languages of the world and some emojis

30
Q

What are images made up of?

A

Pixels

31
Q

The more pixels per inch, the greater the resolution but…

A

The greater the file size since more data needs to be stored

32
Q

Colour depth

A

The number of bits per pixel

33
Q

The more colours represented in an image…

A

The more bits needed per pixel and therefore the greater the file size

34
Q

Metadata

A

Data about data e.g. file type, time and date of creation, author, file size, image dimensions, image resolution, colour depth

35
Q

What is used to log sound in binary form?

A

Analogue-to-Digital Converter

36
Q

Sample resolution

A

The number of bits used to stored each sample

37
Q

The greater the sample resolution…

A

The greater the accuracy and therefore quality but also file size

38
Q

Sample rate

A

Frequency in Hz with which sound is recorded

39
Q

The greater the sample rate…

A

The greater the quality and file size

40
Q

Features of lossy compression

A
  • Removes data that can go unrecognised to the user
  • Less accuracy
  • Smaller file size
  • Used for images (jpg), audio (mp3), video and GIFs
41
Q

Features of lossless compression

A
  • Identifies and encodes repeated sections of data so that they can be represented efficiently
  • More accuracy
  • Larger file size
  • Used for documents and PNGs

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