Storage Devices ( 2 )

Question 1

Why may USBs be used?

Answer 1

Transferal of data between computers.

Question 2

What are the three types of optical disk?

Answer 2

• Read Only, CD-ROM
• Recordable, CD-R
• Re-writable, CD-RW

Question 3

How do optical disks work?

Answer 3

• High powered laser is used to burn sections of its surface, making them less reflective.
• A laser at a lower power is used to read the disk by shining light onto the surface, and a sensor is used to measure the amount of light that is reflected back.
• Has At the point where a pit starts or ends, light is scattered and therefore not reflected as well.
• Reflective and non reflective areas are read as 1s and 0s.

Question 4

How does a CD ROM work?

Answer 4

• Has pits in its surface that have been done beforehand.

Question 5

What are lands?

Answer 5

Areas that have not been pitted.

Question 6

What are some advantages to using optical disks?

Answer 6

• Cheap to manufacture and distribute
• Robust during carriage
• Lightweight

Question 7

What are the functions of each CD format?

Answer 7

• CD-ROM is pressed at the time of manufacture
• CD-R can be written to once
• CD-RW can be written, read many times, erased and written again.

Question 8

What are some uses for each of the CD formats??

Answer 8

• CD-ROM can be used for packaging and mailing software
• DVD can be used for storing video data, such as movies
• CD-RW can be used for transferal of files between computers.
• CD-R can be used for copying data.

Question 9

How do recordable disks work?

Answer 9

• They use a reflective layer with a transparent dye coating that becomes less reflective when a laser burns a spot in the track.

Question 10

What parts make up an SSD?

Answer 10

• Array of chips arranged on a board.

* comprised of millions of NAND flash memory cells, and a controller which manages pages & blocks of memory.

Question 11

How do SSDs work?

Answer 11

• Each cell works via delivering a current along the bit and word lines to activate the flow of electrons ( current ) from the source towards the drain.
• Current on the word line is strong enough to force a few electrons across an insulated oxide layer into a floating gate.
• Once the current is turned off, electrons are trapped.
• State of NAND cell is determined via measuring charge in the floating gate, zero charge = 1, some charge = 0.

Question 12

How do HDDs work?

Answer 12

• Rigid rotating platter coated with magnetic material.
• Iron particles are polarised to become either north or south states, which represent 0 and 1.
• Disk is divided into tracks in concentric circles, each track subdivided into sectors.
• Disk spins very quickly.
• Drive head moves across the disk to access different tracks & sectors.
• Data is read or written tot he disk as it passes under the drive head.

Question 13

What happens to the head when it is not in use?

Answer 13

Parked to one side of the disk in order to prevent damage from movement.

Question 14

What are some advantages of HDDs?

Answer 14

• Huge Capacity

* Low Cost

Question 15

What are some disadvantages of HDDs?

Answer 15

• Less portable

* Not as durable as other alternate means of secondary storage.