Chapter 3 Hardware: Unit 3.3: Data Storage

Question 1

What are the 2 groups of memory and storage devices?

Answer 1

Primary memory
Secondary storage

Question 2

Define primary memory

Answer 2

RAM and ROM
Directly accessible by the CPU

Question 3

Define internal secondary storage

Answer 3

Hard disk drive (HDD)
Solid state drive (SSD)

Not directly addressed by the CPU
All are non-volatile devices
Can be internal or external to the computer

Question 4

Define external secondary storage

Answer 4

DVD/CD and DVD-RAM
Blu-ray disc
USB memory stick/ flash memory
Removable hard drive

Not directly addressed by the CPU
All are non-volatile devices
Can be internal or external to the computer

Question 5

Define RAM

Answer 5

Random Access Memory
Can be written to or read from, and the data can be changed by the user or the computer i.e. it is a temporary memory
Used to store data, files, part of an application or part of the operating
system currently in use
It is volatile, which means memory contents are lost when powering off the computer

Question 6

What are the two types of RAM?

Answer 6

DRAM and SRAM/ Dynamic RAM and Static RAM

Question 7

Define DRAM

Answer 7

Each DRAM chip consists of transistors and capacitors. Each of these parts is tiny since a single RAM chip will contain millions of transistors and capacitors. The function of each part is:
- capacitor – this holds the bits of information (0 or 1)
- transistor – this acts like a switch; it allows the chip control circuitry to read the capacitor or change the capacitor’s value.
This type of RAM needs to be constantly refreshed
If it wasn’t refreshed, the capacitor’s charge would leak away very quickly leaving every capacitor with the value 0.

Question 8

What is the advantages of DRAM over SRAM?

Answer 8

They are much less expensive to manufacture than SRAM
They consume less power than SRAM
They have a higher memory capacity than SRAM

Question 9

Define SRAM

Answer 9

Doesn’t need to be constantly refreshed
It makes use of flip flops, which hold each bit of memory.
Faster than DRAM
DRAM is the most common type of RAM used in computers, but where absolute speed is essential, for example, in the CPU’s memory cache, SRAM is the preferred technology
Memory cache is a high-speed portion of the memory; it is effective
because most programs access the same data or instructions many times.
By keeping as much of this information as possible in SRAM, the computer avoids having to access the slower DRAM.

Question 10

Define ROM

Answer 10

Read-Only Memory

They are non-volatile
They are permanent memories
The contents can only be read
They are often used to store data that the computer needs to access when powering up for the first time (the basic input/output system (BIOS)); these are known as the start-up instructions (or bootstrap)

Question 11

What are the 3 categories of secondary storage?

Answer 11

Magnetic
Solid State
Optical

Question 12

Define HDD

Answer 12

Hard Disk Drive
Data is stored in a digital format on the magnetic surfaces of the disks called platters
Read-write heads consist of electromagnets that are used to read data from or write data to the platters and can move very quickly
A number of read-write heads can access all of the surfaces of the platters in the disk drive
Normally each platter will have two surfaces which can be used to store data, which is stored in sectors and tracks.
HDDs have very slow data access
The effects of latency then become very significant
When a file or data is stored on a HDD, the required number of sectors needed to store the data will be allocated, but cannot be adjacent to each other
All data in a given sector on a HDD will be read sequentially, however, access to the sector itself will be by a direct read/write head movement
Removable hard disk drives are essentially HDDs external to the computer that can be connected to the computer using one of the USB ports.

Question 13

Define platters

Answer 13

Data that is stored in a digital format on the magnetic surfaces of the disks
Platters can be made from aluminium, glass or a ceramic material.

Question 14

Define sector

Answer 14

A sector on a given track will contain a fixed number of bytes.

Question 15

Define latency

Answer 15

The time it takes for a specific block of data on a data track to rotate around to the read-write head in an HDD

Question 16

Define SSD

Answer 16

Solid state drives (SSD) remove the latency issue considerably since they have no moving parts and all data is retrieved at the same rate. Don’t rely on magnetic properties
Store data by controlling the movement of electrons within NAND or NOR chips.
The data is stored as 0s and 1s in millions of tiny transistors (at each junction one transistor is called a floating gate and the
other is called a control gate) within the chip.
This effectively produces a nonvolatile rewritable memory.

Question 17

Define floating gate and control gate transistors

Answer 17

Floating gate and control gate transistors use CMOS (complementary metal oxide semi-conductor) NAND technology. Flash memories make use of a matrix; at each intersection on the matrix there is a floating gate and a control gate
A dielectric coating separates the two transistors, which allows the floating gate transistor to retain its charge
The floating gate transistor has a value of 1 when it is charged and a value of 0 when it isn’t.
To program one of these ‘intersection cells’ a voltage is applied to the
control gate and electrons from the electron source are attracted to it. But due to the dielectric coating, the electrons become trapped in the floating gate.

Question 18

What are the benefits of the newer technology in SSDs?

Answer 18

More reliable
Lighter
Don’t have to ‘get up to speed’ before working properly
Lower power consumption
Cooler than HDDs
Very thin
Data access is considerably faster than HDDs

Question 19

What is the main drawback of an SSD?

Answer 19

The longevity of the technology

Question 20

Name an example of technology that uses SSD technology,

Answer 20

Memory sticks/flash memories

Question 21

Name 3 examples of optical storage devices.

Answer 21

CDs, DVDs and Blu-ray discs

Question 22

Describe CDs and DVDs and how they work.

Answer 22

Both use a thin layer of metal alloy or light-sensitive organic dye to store data.
Both systems use a single, spiral track which runs from the centre of the disk to the edge.
When a disk spins, the optical head moves to the point where the laser beam ‘contacts’ the disk surface and follows the spiral track from the centre outwards.
A CD/DVD is divided into sectors allowing direct access to data.
The outer part of the disk runs faster than the inner part of the disk.
The data is stored in ‘pits’ and ‘lands’ on the spiral track.
A red laser is used to read and write the data. CDs and
DVDs can be designated ‘R’ (write once only) or ‘RW’ (can
be written to or read from many times).

Question 23

What are the differences between CDs and DVDs?

Answer 23

The potential for dual-layering, which considerably increases the
storage capacity.
Two layers of a standard DVD are joined together with a transparent spacer, and a very thin reflector is also sandwiched between
the two layers.
Reading and writing of the second layer is done by a red laser focusing at a fraction of a millimetre difference compared to the first layer.
Standard, single layer DVDs still have a larger storage capacity than CDs because the ‘pit’ size and track width are both smaller. This means that more data can be stored on the DVD surface.
The shorter the wavelength of the laser light, the greater the storage capacity of the medium.

Question 24

What are the differences between DVD and Blu-ray?

Answer 24

A blue laser, rather than a red laser, is used to carry out read and write
operations
Using blue laser light means that the ‘pits’ and ‘lands’ can be much smaller
Blu-ray can store up to five times more data than normal DVD
Single-layer Blu-ray discs use a 1.2 mm thick poly carbonate disk; however, dual layer Blu-ray and normal DVDs both use a sandwich of two 0.6 mm thick disks
Blu-ray disks automatically come with a secure encryption system that helps to prevent piracy and copyright infringement
Blu-ray discs have a faster data transfer rate than DVDs

Question 25

What 6 actions are possible with Blu-ray discs?

Answer 25

Record high definition television programs
Skip quickly to any part of the disc
Create playlists of recorded movies and television programmes
Edit or re-order programs recorded on the disc
Automatically search for empty space on the disc to avoid over-recording
Access websites and download subtitles and other interesting features

Question 26

What are the benefits of virtual memory?

Answer 26

Programs can be larger than physical memory and still be executed
There is no need to waste memory with data that isn’t being used
Reduces the need to buy and install more expensive RAM memory

Question 27

What is the main drawback of using virtual memory?

Answer 27

Disk thrashing.

Question 28

Define cloud storage

Answer 28

Method of data storage where data is stored on remote
servers.

Question 29

Define data redundancy

Answer 29

The same data is stored on more than one server in case of maintenance or repair, allowing clients to access data at any time.

Question 30

What are the 3 systems of cloud storage

Answer 30

Private cloud
Public cloud
Hybrid cloud

Question 31

Define public cloud

Answer 31

This is a storage environment where the customer/client and cloud storage provider are different companies

Question 32

Define private cloud

Answer 32

This is storage provided by a dedicated environment behind a company firewall; customer/client and cloud storage provider are integrated and operate as a single entity

Question 33

Define hybrid cloud

Answer 33

this is a combination of public and private cloud; some data resides in the private cloud and less sensitive/less commercial data can be accessed from a public cloud storage provider.

Question 34

What are the benefits of using cloud storage?

Answer 34

Customer/client files stored on the cloud can be accessed at any time from any device anywhere in the world provided internet access is available
No need for a customer/client to carry an external storage device with them, or even use the same computer to store and retrieve information
The cloud provides the user with remote back-up of data with obvious benefits to alleviate data loss/disaster recovery
If a customer/client has a failure of their hard disk or backup device, cloud storage will allow recovery of their data
The cloud system offers almost unlimited storage capacity

Question 35

What are the drawbacks of using cloud storage?

Answer 35

If the customer/client has a slow or unstable internet connection, they would have many problems accessing or downloading their data/files
Costs can be high if large storage capacity is required; it can also be expensive to pay for high download/upload data transfer limits with the customer/client internet service provider (ISP)
Potential failure of the cloud storage company is possible – this poses a risk of loss of all back-up data