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Computer science > 1.2 – Memory and storage > Flashcards

1.2 – Memory and storage Flashcards

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1
Q

What are the differences between RAM and ROM?

A

RAM
* Volatile
* Read and write
* Size - a few GB
* Slotted into sockets - easily updated
* Holds instructions and data

ROM
* Non-volatile
* Read only
* Size - a few MB
* Soldered into motherboard - hard to update
* Holds basic computer hardware settings*

* In the past held BIOS

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2
Q

What is primary storage for?

A

To hold both data and programs that are in current use by the CPU.

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3
Q

What does primary storage consist of?

A

RAM and ROM

Registers, the cache and the external cache are also part of it.

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4
Q

How fast is primary storage?

(Compared to secondary storage)

A

Primary storage is about 200 times faster than secondary storage.

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5
Q

What is volatile memory?

A

A type of memory that loses its data once power to the memory chip is switched off.

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6
Q

Give examples of volatile and non-volatile memories.

A

Volatile memory includes RAM, CPU registers and the cache.

Non-volatile memory includes ROM and secondary storage.

Secondary storage is never volatile.

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7
Q

What is RAM used for?

A

RAM is used as main memory. It acts as a temporary store for program instructions and data.

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8
Q

How much RAM is needed for an avarage computer?

A

4GB - 8GB

Windows 10 needs a minimum of 2GB of RAM just to run.
A budget laptop typically includes 4GB of RAM. This is enough for running some basic email, a browser and perhaps a word processor or movie player.
If you intend to run memory hungry applications such as computer games or image processing software you will more than likely need a minimum of 8GB.

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9
Q

What is ROM for?

A

ROM holds the start-up instructions for the computer. It is read-only. It cannot be written to.

ROM stands for Read Only Memory.

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10
Q

What is virtual memory?

A

Virtual memory is sections of secondary storage which are used as main memory.

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11
Q

What are some problems with excess use of virtual memory?

A

Disk Thrashing - The disk can get damaged as it is constantly being used.
The computer will run slower as virtual memory is much slower than RAM.

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12
Q

What are the three types of secondary storage?

A
  • Optical storage
  • Magnetic
  • Flash
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13
Q

What is the purpose of secondary storage?

A

To save data once the computer is turned off.

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14
Q

What is meant by a secondary storage device?

A

A non-volatile device that stores data permanently.

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15
Q

What are the criteria which should be used when choosing a secondary storage device?

A
  • Capacity
  • Speed
  • Portability
  • Durability
  • Reliability
  • Cost
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16
Q

What is meant by storage media?

A

The physical object used to store the data.

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17
Q

How does magnetic storage work?

A

It changes the state of minute magnetic particles or ‘domains’ to store data.

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18
Q

What are the advantages of magnetic storage?

A
  • High capacity.
  • Low cost per gigabyte*
  • High speed
  • Random access to data
  • Reliable**

*Magnetic tape is the cheapest, but hard disk is very low as well.
**Magnetic tape can hold its data for up to thirty years in the correct environment.

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19
Q

What are the disadvantages of magnetic storage?

A
  • Not very portable
  • Has mechanical moving parts
  • Data can be lost near strong magnetic fields
  • Data read \ write is not as fast as flash technology
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20
Q

How is optical storage read?

A

A lazer detects is there is a pit or not. Those two states translate to a 1 or 0.

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21
Q

How is optical storage written to?

A

A lazer burns pits into the disc.

22
Q

What are some advantages of optical storage?

A
  • Cheap if less than 10GB needs to be stored
  • Portable
  • Ideally sized for storing movies and videos.
  • Immune to magnetic fields.
23
Q

What are some disadvantages of optical storage?

A
  • Not cheap if terabytes need to be stored
  • Not as portable as Flash media
  • Slow to write (burn) to and much slower than hard disk to access.
  • Easily scratched
  • Cannot write over stored data
24
Q

Give some examples of flash memory.

A
  • USB memory sticks
  • Solid State Drives
  • SDHC memory cards (as found in digital cameras)
25
Q

How does flash memory hold data?

A

Solid state media hold data using electronic switches. Open switch = 1, closed switch = 0.

26
Q

List some advantages of flash memory.

A
  • Very portable in the form of SD memory cards and USB memory sticks.
  • Large capacity, especially in the form of a SSD.
  • Very tough and robust
  • Faster than hard disk as no mechanical parts are needed.
  • Solid State Drives are silent unlike hard disks.
27
Q

What would magnetic tape be used for?

A

Data archiving. (100s of TB)

28
Q

What is reliability?

A

The shelf life of the media. How long it will retain data so that it can be accessed reliably and without error in the format in which it was originally saved.

29
Q

What is a bit?

A

A 1 or 0

30
Q

What is a byte?

A

8 bits

31
Q

What is a kilobyte?

A

1000 bytes

32
Q

What is a nibble?

A

4 bits

33
Q

How much text can a KB store?

A

1000 characters. About this length:

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Nam a justo pretium, ornare elit vitae, consequat turpis. Pellentesque ante ex, mollis sed augue ac, tempor laoreet nunc. Vivamus interdum ligula sed tellus ornare tristique. Sed sagittis vestibulum metus, sit amet consequat lacus lacinia nec. Suspendisse potenti. Quisque egestas sapien leo, eget egestas leo finibus dictum. Cras auctor molestie nibh, quis sagittis est auctor id. Nam congue, est ac aliquam auctor, odio metus gravida orci, sit amet interdum tortor mauris ac ex. Mauris a velit lorem. Suspendisse at lacinia velit, blandit porttitor leo. Sed cursus augue sit amet massa lacinia nunc.

34
Q

What can a MB store?

A

About 300 essays of text.

A powerpoint presentation is usually a few MB.
A typical MP3 song is between 3 - 5 MB in size.
A CD can store 650 MB

35
Q

How much can a GB store?

A

About 10 meters of books on a shelf.
A Hollywood blockbuster film is about 4-8 GB - it can be stored on a DVD.

36
Q

How much can a TB store?

A

150 complete high definition movies

37
Q

How much can a PB store?

(Petabyte)

A

Data centers and supercomputers use petabytes of memory.

38
Q

Why is data stored in binary?

A

Computers can only use binary.
Therefore everything, every piece of data has to be converted to binary.

39
Q

What is binary overflow?

A

When the computer performs a shift or a operation on a binary number and loses some information because there isn’t enough space for all the information.

When overflow occurs,

40
Q

What is a ‘flag’?

A

A ‘flag’ is a single bit within a certain register and is used to mark an event happening.

41
Q

What is ASCII?

A

It provides a way to convert standard letters, numbers, and punctuation into binary.

42
Q

How many characters are there in the ASCII character set?

A

127

43
Q

What is a character set?

A

A character set is the mapping between characters and their identifying code values.

44
Q

How many characters are there in the Unicode character set?

A

65535

It uses a 2 byte system.

45
Q

What is the extended ASCII set?

A

ASCII with an extra 128 characters. It uses a 1 byte (8-bit) system.

46
Q

Why do we compress files?

A
  • Less storage space required for files
  • Faster download and uploads
  • Smaller file attachments for email
  • Coping with slow links when streaming
47
Q

What is lossy compression?

A

Compression where some data is lost.

48
Q

What is lossless compression?

A

Compression where no data is lost.
It works by rearranging the data to store it more efficiently.

49
Q

What is the compression ratio?

A

R = original file size / compressed file size

50
Q

How does lossless file compression work?

A

It works by finding patterns in a file and storing it more efficiently.

51
Q

How does lossy compression work?

A

By eliminating the less relevent aspects of the information.
For example, to compress an image, the resolution and colour depth might be reduced.

Text files can usually not be compressed by lossy compression, because the loss of a character might obfuscate the meaning of the sentence. This doesn’t matter as text files are usually very small.

Computer science (3 decks)

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