6. Memory and data storage

Question 1

How does a midi file work?

Answer 1

Consists of list of commands that instruct a device how to produce a particular sound or musical note.
Each midi command has a particular sequence of bytes. The first byte is the status byte which tells the device which function to perform and the midi channel which is a number between 0 and 15.
Examples of commands include note on or off or key pressure.
Two additional bytes are required – the pitch byte and velocity byte (tells device how loud to play not how fast).
When the midi file is played back through a device it is played in an identical way to the original.
To play it though an instrument you need a sequencer software as the guitar won’t understand the instructions.

Question 2

Why use a midi file?

Answer 2

Smaller size than mp3

Plays music back the same way as the original.

Question 3

How does an mp3 file work?

Answer 3

Uses lossy compression algorithms with perceptual music shaping which remove sounds the human ear cannot hear properly to reduce file size.

Question 4

What is the difference between mp3 and mp4?

Answer 4

mp4 allows storage of multimedia files such as music, videos and photos whereas mp3 only stores sound.

Question 5

How can text documents be compressed?

Answer 5

Common repeated words and word sections can be put in a data dictionary and replaced by numbers.

Question 6

What is the difference between lossy and lossless compression?

Answer 6

In lossless sections of data are reconstructed when the file is uncompressed whereas in lossy compression sections of data are deleted.

Question 7

What are the features of RAM?

Answer 7

Volatile
Stores parts of the os currently in use
Contents can be changed

Question 8

What type of storage do buffers commonly use?

Answer 8

RAM

Question 9

What are the advantages of DRAM?

Answer 9

Cheaper
Consume less power
Higher storage capacity

Question 10

What are the advantages of SRAM?

Answer 10

Doesn’t need to be constantly refreshed.

Faster

Question 11

How does DRAM work?

Answer 11

Contains capacitors (store data) and transistors (allows computer to change value in capacitor)

Question 12

Why does DRAM have to be refreshed?

Answer 12

The charge leaks away from the capacitors so all would be left with the value 0.

Question 13

How does SRAM work?

Answer 13

Uses ‘flip-flops’ which hold each bit of memory.

Question 14

What are the features of ROM?

Answer 14

Non volatile
Stores the boot code
Contents cannot be changed

Question 15

How does a hard disk drive work?

Answer 15

Data is stored on the magnetic surfaces (usually two surfaces) of a number of disks in tracks (areas going round the disk) and sectors. The disks spin and read-write heads can access all of the surfaces on the disk.

Question 16

What is the main disadvantage of HDDs?

Answer 16

Can be slow as many applications require the read-write heads to constantly look for the right data. This leads to problems with latency (the time taken for a block of data to rotate to the read-write head).

Question 17

What are the advantages of SSDs over HDDs?

Answer 17

SSDs have no moving parts - more reliable
Lighter
Don't have to 'get up to speed'
Use less power
Run cooler
Very thin
Faster

Question 18

What is the main disadvantage of SSDs?

Answer 18

Questionable longevity

Question 19

What is the difference between flash and EEPROM?

Answer 19

Flash uses NAND chip, EEPROM uses NOR chips.
EEPROM is more expensive.
EEPROM allows data to be read or erased one byte at a time whilst flash only allows data to be manipulated in blocks.

Question 20

How do CDs and DVDs work?

Answer 20

Use a thin layer of metal alloy or light sensitive dye to store the data in a spiral. A red laser is used to read and write the data is ‘pits’ and ‘bumps’ in the track.

Question 21

What is the difference between CDs and DVDs?

Answer 21

DVDs have a higher storage as they use dual layering. This means there are two recording layers, one above the other with a transparent spacer and thin reflector in between. A second red laser is used to read and write the second layer.
DVDs also use a smaller wavelength of light which means the ‘pits’ and ‘bumps’ are smaller so more data can be stored.

Question 22

How does a DVD-RAM disc work?

Answer 22

Uses concentric tracks
Allows read and write operations to happen simultaneously
Allow more read and write operations
Have great longevity

Question 23

What is the difference between DVD and Blu-ray?

Answer 23

Blu-ray uses a blue laser so has a greater capacity.
Uses a single layer so stops birefringence (where light is refracted into two beams causing errors)
Automatically comes with secure encryption system which helps to prevent piracy.

Question 24

Advantages of using USB flash memory

Answer 24

Small and lighweight
Can be used as a dongle (contains extra applications that must be used for software to work)
No moving parts

Question 25

What is the main disadvantage of using flash memory?

Answer 25

Have to wait for message before removing as otherwise data may become corrupted.

Question 26

How much storage does one ASCII character take up?

Answer 26

One byte

Question 27

How much storage does one pixel take up?

Answer 27

Three bytes