3.7.4.2 Secondary Storage Devices.

Question 1

What is a computers primary storage?

Answer 1

Memory such as RAM or ROM.

Question 2

What is a computers secondary storage?

Answer 2

Use to store files and applications, includes HDD’s, SSD’s and optical disks.

Question 3

What does a HDD consist of?

Answer 3

A number of circular platters which are made from magnetic material. Above each platter hovers an actuating arm on which is a read/write head.

Question 4

What does the actuating arm allow for (HDD)?

Answer 4

The actuating arm allows the read/write head, which changes the magnetic polarity of parts of the platter, to access all portions of each platter.

Question 5

How is data written in HDD’s?

Answer 5

In concentric tracks, each of which is further divided into sectors.

Question 6

Why do HDD’s have good read/write speeds?

Answer 6

The platter rotates thousands of times per minute, allowing for good read and write speeds.

Question 7

What is the typical HDD size?

Answer 7

Between 500GB and 5TB.

Question 8

How can we increase the capacity of a HDD whilst still keeping it the same size?

Answer 8

Adding more platters and decreasing the width of the tracks.

Question 9

Why are HDD’s susceptible to damage?

Answer 9

Because of the number of moving parts in hard disk drives, they are susceptible to damage from movement. This makes them unsuitable for use in portable devices like phones and tablets.

Question 10

What does a SSD consist of?

Answer 10

NAND flash memory cells and a controller than manages the structure of data on the drive.

Question 11

Is NAND flash memory volatile or non-volatile? What does this mean?

Answer 11

Non-volatile, meaning that an SDD’s contents are retained even when there is no power being supplied.

Question 12

What forms the memory cells of an SSD?

Answer 12

The memory cells are floating gate translators which store information by trapping an electrical charge.

Question 13

How is data stored on an SDD?

Answer 13

In pages, which are combined to form blocks.

Question 14

Can SDD’s overwrite data?

Answer 14

No, instead a controller must completely erase the entirety of a page before writing new information to it.

Question 15

Why do SDD’s have higher read//write speeds than HDD’s?

Answer 15

Because SSDs don’t have any moving parts, they are capable of far higher read and write
speeds than HDDs and are suitable for use in portable devices like phones and tablets.

Question 16

Define an optical disk.

Answer 16

Store information which can be read
optically by a laser.
Can be either:
Read-only.
Recordable.
Rewritable.
Depending on what they are used for.

Question 17

Describe the characteristics of an optical disk.

Answer 17

Disks have stripes called pits; the areas surrounding the pits are known as lands.

Question 18

How are pits created?

Answer 18

Pits are burnt into the disk by a high-power laser which permanently deforms the surface.

Question 19

How many tracks do optical disks have?

Answer 19

Unlike hard-disk drives which use tracks and sectors, optical disks have just one.
continuous track which spirals from the centre of the disk to the outside edge.

Question 20

Outline the process of an optical disk.

Answer 20

Low power laser beam is passed over the flat surface of an optical disk. Reflects back onto a photodiode. However, when the laser is incident on a pit, the light from the beam is scattered in different directions rather than reflected back at the photodiode. The resulting pattern of reflections and scatters can be converted into a digital signal of binary
1s and 0s.

Question 21

What role does opaque dye play in an optical disk?

Answer 21

On recordable and rewritable optical disks, a pattern of reflections and scatters is created not by pits and lands but by an opaque dye on the disk’s surface. Where there is no dye, the disk reader’s laser beam is reflected off of the optical disk’s surface. Where there is dye, the laser beam is absorbed by the dye and not reflected at all.

Question 22

What purpose does photosensitive dye have in an optical disk?

Answer 22

Recordable optical disks use a special photosensitive dye which changes from opaque to
transparent under a high-power laser which is used to write information to the disk. The dye remains unaffected by the low-power laser used to read the disk.

Question 23

Capacity:

1. HDD
2. SDD.
3. Optical disk.

Answer 23

1. High capacity. Typically
   between 500GB and 5TB.
2. Relatively low capacity.
   Typically under 1TB.

3.Very low capacity. Blu-rays
have the highest capacity
at 25GB.

Question 24

Read/Write speeds:

1. HDD
2. SDD.
3. Optical disk.

Answer 24

1. Good speeds.
   ≈ 100MB/s.
2. Very high speeds.
   ≈ 500MB/s
3. Relatively low
   speeds.
   ≈ 30MB/s

Question 25

Latency:

1. HDD
2. SDD.
3. Optical disk.

Answer 25

1. High.
2. Very low.
3. High.

Question 26

Portability:

1. HDD
2. SDD.
3. Optical disk.

Answer 26

1. Bulky, heavy and
   easily damaged by
   movement.
2. Lightweight and rarely
   damaged by
   movement.
3. Very small and
   lightweight, can be
   damaged by scratches
   and dirt.

Question 27

Sustainability:

1. HDD
2. SDD.
3. Optical disk.

Answer 27

1. Good for desktop PCs and servers.
2. Good for laptops,
   phones and tablets.
3. Good for sharing and
   distributing volumes of data.