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Computer Science > 3.5 Memory and storage > Flashcards

3.5 Memory and storage Flashcards

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1
Q

What are the 3 types of storage a computer has?

A
  • Primary Storage
  • Secondary Storage
  • Off-line storage
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2
Q

What does RAM do?

A
  • Primary Storage
  • Can be written to or read from
  • Data is only stored temporarily, and all memory is erased without power, it is volatile
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3
Q

What is an ‘embedded computer’?

A
  • A computer built into another device to carry out one or more specialised tasks
  • eg. a calculator
  • Has not much RAM (few KB)
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4
Q

What is a ‘general purpose computer’?

A
  • The modern form of computer
  • eg. Desktop PC, smart phone
  • Generally has a few GB of RAM
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5
Q

What is ‘ROM’?

A
  • Read Only Memory
  • It does not loose its data when it looses power
  • The ROM holds data that is used to control the device before the system software on start up
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6
Q

What is firmware?

A

ROM that holds programs that run on an embedded computer

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7
Q

What does ‘bootstrap’ mean?

A

ROM that contain start up instructions for the computer

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8
Q

What is ‘EPROM’?

A
  • Erasable Programable Read Only Memory

- ROM that can be erased and re written

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9
Q

What is flashing?

A

The process or erasing and rewriting the programs on ROM

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10
Q

Primary storage…

A
  • Directly accessible by the processor
  • Temporarily stores data
  • Can be read from and written to extremely quickly
  • Normally a few GB capacity
  • Fixed within the computer
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11
Q

Secondary storage…

A
  • Not directly accessible from the processor, data first has to be transferred into RAM
  • Data is permanently stored until it is erased
  • Slower to read and write to than primary storage
  • Can be up to a terabyte or more in capacity
  • Some secondary storage devices are removable
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12
Q

What are the 3 types of secondary storage?

A
  • Magnetic
  • Optical
  • Solid-state
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13
Q

What is magnetic storage?

A
  • Read, write and erase data using electromagnets
  • The storage is usually a hard disk or tape with small magnetic dots that can be charged either positively or negatively using electromagnets, this is binary data
  • Tape based storage use a cartridge of looped magnetic tape that passes over an electro magnet to read/write/erase data, however data is stored serially and isn’t good for saving files to
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14
Q

Explain how disk based magnetic storage works…

A
  • There are several disks called platters
  • The platters can be made from metal or glass
  • They have a magnetised coating on which the data is stored
  • Dots lie in the tracks that run around each platter
  • All platters are on a spindle
  • Spindle rotates at high speed
  • The dots pass under a moving electromagnetic arm
  • The arm moves back and forth across the platters to access data from different tracks
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15
Q

What is the ‘data transfer rate’?

A

The speed at which data can be moved to and from a storage device

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16
Q

Explain how optical storage works…

A
  • Shines a laser onto plastic disks
  • The disks have an aluminium coating to make them reflective
  • The surface of the disk has one large track the spirals out from the centre
  • Data is stored on the track using a laser to make PITS and the are between the pits is called LAND, these to areas reflect light back differently are represent the binary
  • The number 11101001 would be pit;pit;pit;land;pit;land;land;pit
  • They have a good data transfer speed
17
Q

CD and DVD acronyms…

A

Compact Disk
Digital Versatile Disks

DVD’s use a higher frequency laser than CD’s and mean that the land and pits can be closer together and smaller on a DVD meaning more data can be stored on a disk of the same physical size.

18
Q

CD capacity

A

700MB

19
Q

DVD Single Layer capacity

A

4.7GB

20
Q

DVD Dual Layer capacity

A

9.4GB

21
Q

Blu-ray Single Layer capacity

A

25GB

22
Q

Blu-ray Dual Layer capacity

A

50GB

23
Q

Blu-ray Triple Layer capacity

A

100GB

24
Q

Blu-ray Quadruple Layer capacity

A

128GB

25
Q

Difference between R and RW with optical disks?

A

R:

  • Comes empty
  • Can be written to once
  • Data can be read multiple times

RW:

  • Can be written to and read from repeatedly
  • High power lasers can be used to make the surface flow and fill the pits, effectively wiping the disk and allowing it to be written to again
26
Q

What is ‘solid state’ storage?

A
  • No moving parts
  • Very very fast read and write speeds
  • Uses flash memory
  • Physically small
  • 230 Megabytes per second
  • Up to 4TB
  • More expensive to produce than magnetic and optical equivalents
  • Uses low power
  • Ideal for portable/handheld devices
27
Q

5 factors in deciding which type of secondary storage device is required….

A
  • Capacity
  • Transfer speeds
  • Portability
  • Durability
  • Cost

Computer Science (21 decks)

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