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Computing > 1.2 Memory and storage > Flashcards

1.2 Memory and storage Flashcards

1
Q

Why do we need primary storage

A

For faster access speed. Reading and writing from a hard disk is is a very slow compared to the speed of the processor so we use RAM to act as a temporary storage for programs and data while the program is being executed by the CPU

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2
Q

Key characteristics of ROM

A
  • non-volatile
  • used to store the bootstrap loader which is required to start up the computer
  • memory can only be read NOT written to
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3
Q

Key characteristics of RAM

A
  • Volatile
  • Stores the user data/programs that are currently in use
  • memory can be both read and written to
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4
Q

Why is virtual memory needed

A

Sometimes when RAM isn’t big enough to hold all the open programs and data in use, virtual memory will be used. This is a small section of the hard disk that is used like RAM. However, in order for the programs or data to be used, they have to be switched back over into RAM which is time consuming and can cause disk thrashing.

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5
Q

Why is secondary storage needed

A

Because ROM is read only and RAM is volatile

  • storage of programs and data when the computer is turned off
  • backup and archive of data files
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6
Q

What are the 3 common types of storage

A
  • Optical
  • Magnetic
  • Solid State
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7
Q

What is the portability of secondary storage

A

How easily it can be unplugged and carried away, whether it fits in a pencil case or needs a larger bag

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8
Q

What is the durability of secondary storage

A

how easily it can be damaged

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9
Q

What is the reliability of secondary storage

A

how long it will last

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10
Q

Advantages and disadvantages of Magnetic storage (6)

A
  • very large capacity
  • faster than optical but slower than SSD
  • not very portable as they are either built into the computer or would fit into a very large pocket
  • not durable due to moving parts
  • very reliable as they can write to the disk an infinite number of times
  • relatively cheap per unit of storage
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11
Q

Advantages and disadvantages of Solid State storage (6)

A
  • medium capacity
  • very fast speed
  • very portable (light and thin)
  • Very durable
  • very reliable
  • considerably more expensive than other types
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12
Q

Advantages and disadvantages of Optical storage (6)

A
  • Small capacity
  • Quite slow
  • very portable
  • scratches can affect data (durability)
  • reliable over medium terms but degrades over time
  • medium cost
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13
Q

Units of data storage in order

A
  • bit
  • nibble
  • byte
  • kilobyte
  • megabyte
  • gigabyte
  • terabyte
  • petabyte
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14
Q

why must data be stored in binary

A

Because the computer understands the 1 to be on or true and the 0 to be off or false

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15
Q

Equation to work out sound file size

A

sound file size = sample rate x bit depth x duration (secs)

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16
Q

Equation to work out image file size

A

image file size = colour depth x image height(px) x image width(px)

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17
Q

Equation to work out text file size

A

text file size = bits per character x number of characters

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18
Q

what is an overflow error

A

when two binary numbers are added and the number is valued as more than 255 so the 8 bit binary can no longer store it

19
Q

How are characters represented on a computer

A

as binary

20
Q

What is a character set

A

all the different characters a computer can represent, encoded using a given number of bits

21
Q

Number of bits per character in ASCII and therefore maximum number of characters in the set

A

7
128

22
Q

Number of bits per character in Unicode and therefore maximum number of characters in the set

A

16
65,000+

23
Q

Advantages and disadvantages of Unicode

A
  • wide range of characters available
  • larger amount of storage needed per character
24
Q

How are images represented by binary

A

Every image is a series of pixels and each pixel is a specific colour, represented by a specific code

25
Q

what is the colour depth of an image

A

the amount of bits per colour which affects how many colours in total can be represented

eg a bit depth of two would allow for 4 colours

26
Q

what is the resolution of an image

A

the number of pixels that make up an image

27
Q

What is Metadata

A

basically is data about the data and provides information about the image

28
Q

What types of information does Metadata include

A
  • file type
  • time and date of creation
  • file size
  • creator of the data

and also for a digital image:
- height and width
- resolution
- colour depth

29
Q

what effect does increasing colour depth and resolution have on the file size

A

also increases

30
Q

what is the sample rate and what is it measured in

A

Sampling is a method of converting an analogue sound signal into a set of binary numbers that are then stored in a digital file.

Measured in Hertz (sample per second)

31
Q

How are analogue sounds stored

A
  • You speak into the microphone which records the sound in analogue.
  • It is then passed through an analogue to digital conversion device (ADC) in the sound card which converts it into the digital version.
  • The amplitude is measured at these regular intervals
  • the values are rounded to a level (sample resolution)
  • This is stored in binary
32
Q

Reasons for compressing a file

A

IT REDUCES THE NUMBER OF BITS SO THAT:
- less storage space needed so more can be stored on a storage device
- faster downloads and uploads
- smaller file attachments for email

33
Q

what is compression

A

a way of reducing the size of a file while still keeping as much of the original data as possible

34
Q

How does lossless compression compress the file

A

It reduces the file size without any loss of data by looking for patterns

eg. four purple pixels in a row could be stored as
4 purple

rather than

purple purple purple purple

35
Q

What file types would lossless compression be used for

A
  • text files
  • spreadsheets
  • emails
  • executable programs
36
Q

Are lossy and lossless compression permanent

A
  • lossless = no
  • lossy = yes
37
Q

How does lossy compression compress the file

A

Reduces the file size by throwing away as much of the original data as it can without noticeably affecting the quality of the picture.

eg. decreasing the colour depth by averaging out all the different colours

38
Q

What file types would lossy compression be used for

A
  • images
  • sound
  • video
39
Q

3 types of lossy formats

A
  • JPEG
  • MPEG
  • MP3
40
Q

2 types of lossless formats

A
  • PDF
  • GIF
41
Q

what is unicode

A

the new standard for representing the characters of all the languages in the world such as Chinese, Arabic etc

42
Q

what is sample resolution

A

the number of bits used to store each sample

43
Q

what is the storage capacity of a single CD

A

640MB

44
Q

what is the storage capacity of a single layer DVD

A

4.7GB

Computing (15 decks)

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