Chapter 1 Types and components of computer systems

Chapter 1 Types and components of computer systems

What is hardware?
In basic terms, hardware is the physical components of a computer
system. The stuff you can touch, basically. Things like a mouse, a
keyboard, a monitor; these are all examples of hardware

What is software?
Software is the programs that control the computer. Things like
Microsoft Word and Google Chrome are examples of software
(Although you should NEVER use brand names like this when
answering exam questions)

Types of software
There are two main categories that software falls into. These
are application and system. Application software is programs that
allow the user to perform tasks. These tasks can be anything from
editing a document in word-processing software to streaming video on
a web browser. System software is programs that allow the computer
hardware to run properly and programs that allow the user to
communicate with the computer. This kind of software can include the
operating system (which is the software that basically allows the user
to interact with the computer, and, without it, using a computer would
be basically impossible), utilities (which manage and control the
computer. Stuff like antivirus and file-backup software), and drivers
(which allow hardware to communicate with the computer’s operating
system).
Chapter 1 Types and components of computer systems

The CPU (Central Processing Unit)

The CPU deals with commands. It is what is in charge of interpreting
and executing the commands. It is often referred to as the “brain” of
the computer as it’s really what controls everything. Without it, the
computer would not be able to function. Similarly, we would not be
able to function without a brain. Known also by the name
“microprocessor“, the CPU tends to be a single circuit board found at
the heart of the computer (sorry about all the body organ comparisons
here…) as well as in common household appliances such as washing
machines.

HDD (Hard Disk Drive)

Also known as SSD (Solid State Drive), the internal HDD is the main
piece of hardware where files are saved to and stored. The good things
about HDD are that it’s fast at transferring and accessing data and that
it has a lot of memory space to save lots of files.

RAM (Random Access Memory)

RAM is different to HDD as it doesn’t save files permanently. RAM is
used to store data for applications that are running on the PC and can
be saved to as well as read from. The data saved to the RAM is deleted
once the PC is turned off which is what is called volatile memory.

ROM (Read Only Memory)

ROM is the opposite of RAM as it saves data that has to be permanent
like the computer’s configuration data. ROM also cannot be read to,
only read from. ROM also saves data even when the PC is turned off.
The ROM also contains the BIOS (Basic Input / Output System), which is
the code that the computer uses while starting up. The BIOS checks to
make sure all of the hardware is there and working when starting up
the computer.
Chapter 1 Types and components of computer systems

CLI (Command Line Interface)

Command Line Interfaces are the ones you stereotypically see in
movies when a person is “hacking” something. Unlike a GUI (which we’ll
get to in a sec), a CLI allows the user to perform actions by typing in
commands instead of clicking on icons. You can see why CLIs are not
the preferred choice of operating system as you have to learn all of the
complicated commands to be able to do anything

Task: If you have a Windows PC, go to search and look for “Command
prompt”. This is an example of a CLI

GUI (Graphical User Interface)

A graphical user interface is the most common type of operating
system. The two biggest operating systems, Windows and macOS, are
both examples of a GUI. The main difference between a GUI and a CLI is
that you control a GUI by clicking icons using a pointer (also known as
the mouse arrow) instead of having to learn complicated codes and
type them in. The easiest way to memorise the basic features of a GUI
is to remember the acronym WIMP which stands
for Windows Icons Menu Pointer
Chapter 1 Types and components of computer systems

Advantages and disadvantages

Command Line Interface:
Advantages:
 The user directly communicates with the computer instead of through a operating
system
 The user is restricted to only the predetermined options of the operating system
that the computer uses
 The user can change the computer’s configuration settings if they want to

Disadvantages:
 The user needs to learn long and complex commands in order to be able to have
any interaction with the computer
 All the commands need to be typed in which can take a long time and it is also
likely that the user will make mistakes when typing in the command

Graphical User Interface:

Advantages:
 The user does not need to learn long and complicated commands to be able to use
the computer
 It is much more user-friendly as the method of using a pointer to click on icons is
far easier to learn than typing in complex codes

Disadvantages:
 The interface takes up a lot more memory space than a CLI interface
 The user can only perform actions that are predetermined by the operating system
that they are using
 It requires an operating system to work which can cost both money and memory
space on the computer

PCs (Desktop computer)

A PC (Personal Computer) is a computer that is made up of four main
components: a mouse, a keyboard, a monitor and a processor unit (the
main part of the PC or the “tower” as some call it).
Chapter 1 Types and components of computer systems

Laptops
Laptops (sometimes called notebooks) are computers which combine
the four main components of a PC into one singular device. This makes
it a lot easier to carry around. They also have an internal battery so
that it does not have to be plugged in constantly

Tablets
Tablets do virtually the same thing as a laptop, but even more
efficiently. Tablets combine the screen and keyboard into a singular
touchscreen which makes the whole device smaller and more portable
than a laptop. Tablets also can have 3G/4G/5G capabilities which allow
the user to access the Internet without a need for WiFi. There are also
devices that are cleverly named phablets. These devices have all of the
features of a smartphone and some of the features of a tablet (i.e.
larger storage space), while being smaller than a tablet, but bigger
than a smartphone.

Smartphones
Smartphones allow users to have a computer experience that they can
fit in their pocket. They allow users to make phone calls and use
applications while on the go. Smartphones also run an operating
system, usually either Android, iOS, or Windows (with Windows being
far less popular than the other two). Smartphones have 3G/4G/5G
functionality that allow them to access the Internet without need for a
WiFi connection as long as they have a connected account with a
mobile network provider. 3G/4G/5G are mobile networks which we will
get into later on.
Chapter 1 Types and components of computer systems

Smartwatches
Smartwatches allow the user to have a computer experience on
something even smaller than a smartphone; something that can fit on
your wrist even. They usually consist of a small touchscreen on a strap
that you wear like a watch. The watch is usually connected to your
smartphone via Bluetooth allowing the wearer to do things read
messages, see notifications, control music and calls, check the weather,
and, of course, check the time, without having to use their phone.
Quite often smartwatches will also have health-monitoring (i.e.
measuring the user’s heart rate), fitness, and GPS capabilities as well.

Mainframe computers
These are the big boys. These computers are extremely powerful as
they are the ones that control applications and services like online
banking. They have to be powerful because they have to process
massive amounts of data every day. They will have multiple CPUs
(Central Processing Units) which allow data to be processed much
faster. They will also have massive amounts of storage space and
internal memory (i.e. some will have hundreds of gigabytes of RAM).

Advantages and disadvantages:

PCs (Desktop computers)
Advantages:
 Best specifications (i.e. faster processing, more powerful, more storage space)
 Do not have to worry about battery capacity as it remains plugged into an outlet
 Best heat dissipation – They are the largest so heat does not get trapped as easily
 Since they are not moved often, there is less risk of them being damaged
 Since they are not moved often, they have to most consistent Internet connection
Chapter 1 Types and components of computer systems

Disadvantages:

 Obviously, they are not portable. You cannot take a desktop PC to work or school
with you
 Whenever you want to use files from your PC while away from it, you will have to
save them to somewhere else (i.e. a memory stick or a cloud storage service)
 They tend to take up a lot more space with wires and a separate monitor, keyboard
and mouse

Laptops:
Advantages:

 Obviously, they are much more portable than PCs and you can easily put them in a
bag and take them with you
 There are no wires that clutter up space (except for the power cable when it needs
to charge)
 Can take full advantage of WiFi since the computer does not have to stay in just
one place
 Their portability allows them to be able to connect to multimedia systems

Disadvantages:

 The fact that they are much smaller makes it easier for them to be stolen
 Since they are not constantly plugged in like a PC, battery life becomes a problem
since you have to constantly carry around a heavy charger cable to be able to
charge it
 Sometimes the keyboard is too small and awkward for some people to use. The
trackpad can also be awkward to use

Tablets:
Advantages:

 Tablets are much faster to turn on than a PC or a laptop

 They are more portable than both a PC and a laptop
 The touchscreen is easier to use and means than other input devices aren’t needed
 Comes with built-in apps like a camera and music player app
 The solid-state tech means that it does not heat up as much as a PC or a laptop, so
overheating becomes less of a problem
 The battery life of a tablet is greater than that of a laptop
 It does not completely turn off when you press the power button, meaning it stays
connected to the Internet and can still get alerts
Chapter 1 Types and components of computer systems

Disadvantages:

 They have a lot less storage and memory than PCs and laptops
 If 3G/4G/5G is used frequently, it can become expensive
 Typing on a touchscreen is typically much slower than typing on a physical
keyboard and you are more likely to make spelling mistakes
 Transferring files between devices is a lot less efficient than on a PC or laptop
 Tablets tend to support less files types than a PC or laptop

Smartphones:
Advantages:

 Much smaller than all 3 previously mentioned devices, so it much easier to carry
with you at all times
 You can make calls and connect to the Internet while away from home or work or
anywhere with an Internet connection
 The Internet can be accessed from anywhere (even without WiFi) as long as the
phone has a SIM card with a mobile network provider
 There are countless apps available that make doing certain tasks much more
efficient than doing them on a PC or laptop
 They have a relatively good battery life compared to laptops

Disadvantages:

 The smaller screen makes things quite difficult to read sometimes and makes tasks
like typing more difficult
 Taking pictures and browsing the Internet drains the battery life quite drastically
 The amount of memory space is a lot smaller than that of a PC or laptop, and
usually about half the size of a tablet
 There are certain things that a smartphone operating system can’t do that a
PC/laptop operating system can
 The small size makes it easier to lose a smartphone or to have it stolen
 Using a mobile network can tend to be much slower than WiFi which can be
irritating at times, especially when trying to stream video or music

Tip: When answering exam questions that ask you to

compare the advantages and disadvantages of certain
devices, always mention what it is you are comparing
the device to (i.e. “is smaller than a laptop“)
Chapter 1 Types and components of computer systems

Artificial intelligence (AI) biometrics:

You probably all know about fingerprint scanners. Quite a lot of you
probably have them on your phones. The biggest problem with them is
that, occasionally, the fingerprint will be denied because it is not in the
same exact position that the original was scanned. This is where AI will
be able to help. With the help of AI, the user’s fingerprint will be saved
every time the scanner is used and the fingerprint is accepted,
increasing the amount of samples in the scanner’s database. This way
the system learns about the user’s fingerprint and, with the larger
amount of samples, the scanner will make far fewer mistakes when
scanning the fingerprint. Similar methods can be used for other
biometric devices such as facial recognition (as people age, their face
changes. AI will help with problems such as glasses or facial hair too).

Vision enhancement:
The two main types of vision enhancement are LVES (Low-Vision
Enhancement Systems) and NVE (Night-Vision Enhancement). LVES are
systems that use headsets connected to a computer that allow
zoomed-in images to be projected in front of the user’s eyes to allow
the user to see them better. The much more common NVE system
(commonly used by the military) is a system which uses infrared and
visible light to produce an image that can be seen in the darkness.

Robotics:
When you think of robots, you probably think of humanoid machines
that can walk and talk and act like humans, and while robots like that
do exist (ok, maybe not the “act like humans” bit… not yet anyway),
the majority of robotics tends to be used in manufacturing things. A
popular type of robotics is drones. Used by both the military and
regular people, drones have a wide range of uses from creating 3D
landscapes for GPS systems to search and rescue missions for natural
disasters.
Chapter 1 Types and components of computer systems

Advantages and disadvantages of robotics:

Advantages:

 Saves people having to waste time and energy doing repetitive and simple jobs
 They can perform tasks that would be risky for people to do (like flying into a
hurricane to observe it)
 They can provide entertainment and even help with simple everyday jobs

Disadvantages:

 They take jobs away from people so there is more unemployment

 There is the fear that, with AI technology, robots could someday overpower
humans
 Robots are incapable of showing emotion
 The potential of a robot is limited only to its programming

Quantum cryptography:
To be able to understand quantum cryptography, we first need to be
able to understand what encryption is. This will be explained in more
detail in a later topic, but for now, encryption is the method of
changing a message to make it illegible to a hacker. If the data gets to
the intended recipient, a key can be used to decrypt the data. It is
important to note that encryption does not stop hacking from
occurring; it only makes it so that, if it is hacked, the hacker won’t be
able to understand it (this is a common mistake made when answering
exam questions). Since hackers are always developing new ways to
decipher encrypted messages, new methods of encryption have to be
made too, one of the strongest currently being quantum encryption.
While most methods of encryption use maths to create an algorithm
that encrypts the data, quantum cryptography uses the power of
physics and the properties of photons to create a basically unbreakable
encryption.
Chapter 1 Types and components of computer systems

CAT (Computer Assisted Translation):

I can imagine almost all of you have used services like Google Translate
before. This is an example of a CAT system. When a document or string
of text is presented to the translation tool, the system first removes
anything that isn’t text (like pictures and tables). What is left over is
then translated according to the language that was selected by the
user.

Advantages and disadvantages:

Advantages:

 When in foreign countries, CAT tools make reading things and communicating with
people far easier
 It can be used to translate full websites to allow the website to be read and used
by far more people from far more countries

Disadvantages:

 Most services will provide a very literal and exact translation, sometimes making it
quite difficult to understand. (For a fun example of this, try putting these Japanese
characters into Google Translate: えぐ. If you add more each time,
i.e. えぐえぐえぐ, you’ll find the results change each time and almost always make
no sense)
 Certain things can prevent the system from producing an accurate translation (i.e.
words with multiple meanings and words with no actual translation)

3D and holographic imaging:

A hologram is a free-standing 3D image that you can see around
created using photographic projections. You’ve all seen them in
movies, but hologram technology is actually advancing relatively
quickly (companies like Kino-mo are already using the technology for
advertising)
Chapter 1 Types and components of computer systems

Holograms can be used for many different things, such as:

 Engineering design (allows them to physically see a 3D version of what they are
designing)
 Architecture (creates a 3D image of the building they are designing)
 Medicine (allows 3D images of organs to analyse easier)
 Cinema (special effects)
 Gaming (special effects)
 Advertising (as previously mentioned)
 TVs (a full 3D experience without the need for glasses)
 Computer memory (already in development, can increase the storage of optical
devices up to 1TB by using the full volume of the storage medium and not just the
surface)
 Optical computers (will be able to work at speeds trillions of times faster than
what we are working with now)

VR (Virtual Reality):
With devices like the HTC Vive and Oculus Rift, you are probably all
familiar with VR devices. How it works is that it uses technology like
headsets, sensor suits, data gloves or helmets to simulate situations or
environments.

VR is currently being used for many different things, such as:

 Military training (removes the risk that may occur if the situation was real)
 Education (provides a more interactive and engaging form of education, like being
able to see into ancient buildings for history for example)
 Health care (aids in diagnostics)
 Entertainment (mostly gaming, creates a more immersive gaming experience)
 Fashion (preparation for fashion shows)
 Real estate (allows people to look around properties without actually having to
visit them)
 Engineering (allows engineers to see how their design will look)
 Sport (helps with improving techniques like golf swings for example)
 Media (special effects)
 Science (allows scientists to visualise things like molecular structures)
Chapter 2 Hardware and software
Chapter 2 Hardware and software

Keyboards:
You should all know what a keyboard is so I shouldn’t have to explain it.
They are used to input data and type commands into the computer.

Advantages:

 Can quickly input text into a document

 Very easy to use

Disadvantages:

 Difficult to use if the user cannot use their arms/wrists (duh…)

 Is much slower than other data entry methods (we’ll get to those in a
bit)
 They are quite large and take up a lot of desk space

Computer mouses:
A mouse is the input device that controls the pointer on the computer.
Again, I hope you are all familiar with using a mouse…

Advantages:

 Faster way of select items on a computer than using a keyboard

 Small size – requires less desk space when compared to a keyboard

Disadvantages:

 Again, difficult to use if the user cannot use their arms/wrists (I’m
detecting a theme here…)
 Quite easy to damage, especially the old roller mouses
 Requires a flat surface to be able to use it

Touchpads:
A touchpad is the pointing device that is used on laptops (although can
also be external). Usually a touch-sensitive pad that the user uses to
control where the pointer on the screen goes by moving their finger
across the touchpad
Chapter 2 Hardware and software

Advantages:

 Touchpads have all the same advantages as regular computer mouses

 Touchpads are integrated into laptops removing the need for an
external mouse. It also means the pointer can be controlled even if
there is no flat surface nearby

Disadvantages:

 Surprise surprise, they cannot be used if the user cannot use the or
arms/wrists
 More difficult to use than a regular computer mouse (i.e. tasks
like dragging and dropping become more difficult)

Trackerball:
A trackerball is a basically a weird looking mouse. Instead of having the
ball on the bottom of the mouse and moving the mouse around to
move the cursor, the ball is on the side or the top and you rotate it with
your finger or thumb to move the cursor. It is generally used by people
with disabilities (i.e. RSI (Repetitive Strain Injury))

Advantages:

 Requires less accuracy than a mouse

 Easier to use by disabled people
 More robust than a mouse
 Needs less desk space than a mouse because you don’t actually have to
move it

Disadvantages:

 Costs more as they are not generally supplied with computers

 The user may need training on how to use it since they are not widely
used
Chapter 2 Hardware and software

Remote control:
A remote control uses infrared signals to control whatever it is
controlling wirelessly. They are usually used for TVs, DVD players,
volume control etc however; they are also used for controlling things
industrially i.e. machinery

Advantages:

 They can be used from a reasonable distance away from the receiver
 Can be used to control hazardous things in industry, meaning the
person controlling it does not need to get close to it and put
themselves at risk

Disadvantages:

 Can’t use your arms? Guess what? YOU CAN’T USE IT!
 There are things that can block the signal from the receiver like walls

Joysticks:
Basically the same as a mouse or trackerball, the user rotates the stick
to control what is on the screen. They can also use the buttons on the
joystick to make selections. They are mostly used in video gaming and
simulators. A similar example to a joystick is a driving wheel. It performs
basically the same thing with the same advantages and disadvantages,
however; instead of rotating the joystick, you rotate a steering wheel
instead.

Advantages:

 It is easier to control what is on the screen than if you were trying to

use a keyboard
 For simulators, it feels more realistic making the experience more
immersive
Chapter 2 Hardware and software

Disadvantages:

 It is more difficult to control a cursor than if you were using a mouse

Touch screens:
I would be very surprised if you didn’t know what a touch screen was. A
touch screen is both an input and output device as it displays as well as
taking inputs. The way it works is that the user control what the screen
displays by selecting thing by tapping the screen, swiping to scroll, or
by using gestures.

Advantages:

 It is faster to input and enter data than using a mouse and keyboard
 It is much easier to use than a mouse and keyboard
 They are very user-friendly and require little to no training to use

Disadvantages:

 It has a limited number of options on what it can do

 If the user has to use it frequently, it can lead to things like muscle
strain and RSI (Repetitive Strain Injury)
 The screen can get dirty from all the touching and swiping, making it
less responsive and difficult to see what it is displaying

Scanners:
A scanner is used to scan hard copies of documents and convert them
into computer-readable images. They can be used to scan photographs,
important documents or books (to ensure they are never lost) etc.

Advantages:

 The images can then be stored and edited once they have been
scanned
 It is faster and more accurate than having to manually type in the data
by hand
 You can recover damaged or destroyed documents if something were
to happen to the original
Chapter 2 Hardware and software

Disadvantages:

 Depending on how good the scanner is, the quality of the scanned
image can be quite bad
 They are not particularly fast at scanning the documents

Digital cameras:
Remember film-based cameras? Yeah, me neither. A digital camera
stores and reads photos to and from an SD card. They connect to a
computer via USB to transfer photos and videos, but can also use WiFi
or Bluetooth.

Advantages:

 Produce better quality photos than traditional cameras

 faster to upload as you don’t have to scan physical photos
 No need to develop film as it is all done digitally
 SD cards can save hundreds to thousands of photos

Disadvantages:

 Need a relatively large amount if knowledge on how to use a computer

to be able to transfer the photos
 Images need to be compressed so they take up less storage space
However, with the introduction of better cameras on smartphones, the
digital camera is slowly becoming obsolete, especially for casual
photographers. For professionals not so much due to lens quality.

Microphones:
Right, so… microphones… You talk into them and they save it. The way
a microphone works is that it uses what is called an Analogue to Digital
Converter (ADC) that converts the analogue data (the voice) into a
format that a computer can understand. The ADC is usually the
computer’s sound card.
Chapter 2 Hardware and software

Advantages:

 It is faster to read the text and save it as audio than to type in the text
by hand
 You can manipulate the audio while it is being recorded, saving the
need to go back and edit it later
 It can be used in voice-activation systems (i.e. in a car) to improve
safety as you are not taking your eyes off the road to use your phone

Disadvantages:

 Audio files are usually quite large and take up a lot of storage space
 Voice recognition isn’t as accurate as typing in what you need

Sensors:
Sensors use ADCs (Analogue to Digital Converters) to change the
physical quantity (i.e. temperature or moisture level) into a form that a
computer can understand. Sensors are used to both monitor and
control. When sensors are being used to monitor, they measure the
quantity and save the data to a spreadsheet that is saved on the
connected computer system.

Advantages:

 They take more accurate readings than a human

 Sensors do not have to take breaks so they can measure continuously
 Since the whole system is automatic, there is no need for a human to
have to interfere. This can be helpful if the quantity that is being
measured is dangerous (i.e. acidity of a substance)

Disadvantages:

 If there is something wrong with the sensor, it can mess up all the data
that is saved to the computer system (for example, if the sensor gets
dirty)
Chapter 2 Hardware and software

Graphics tablets:
Graphics tablets are quite similar to regular tablets except they are
used solely for drawing. They do not have an operation system and
cannot be used without being connected to a computer (although
nowadays there are graphics tablets that have the computer built-in,
making them more like laptops). They are used for digital drawings,
computer graphics and are even used instead of typing in countries like
China and Japan where they have complicated characters.

Advantages:

 You can easily undo and modify drawings

 They are a much more accurate methods of drawing than using a
mouse or trackerball
 They can detect pressure, so the brush stroke on the screen depends
on how hard the user presses down with the stylus, making it very
similar to drawing with a real pencil or pen

Disadvantages:

 They are much more expensive than a computer mouse or trackerball

 It generally takes longer to produce a drawing than with traditional
pen and paper
 Sometimes the menus are not user-friendly
 It can be expensive to produce big drawings (i.e. A4, A3…)
 The screen can be easily damaged

Webcams:
Webcams are basically digital cameras that do not save videos and
images. Instead, the videos and images are displayed on a connected
computer and are either used to stream video (i.e. for a video call) or to
save videos and pictures not to the webcam itself, but to the storage
device of the connected computer.
Chapter 2 Hardware and software

Advantages:

 They do not have to be turned off. They can stay on and only be
activated when they’re needed. This is helpful for using immediate
video calls (you do not have to waste time setting up the webcam)
 Their use for video calls allows people to have face-to-face
conversations without having to waste time and money travelling

Disadvantages:

 They are extremely limited in what they can do

 Quite often they produce low quality images
 They have to have a computer to be connected to

Light pens:
These are pens that allow you to select things and interact with
monitors that aren’t touchscreens. The way they work is that the pen
has sensors that detect changes in light. The computer uses this to
detect the pens position on the screen by refreshing the screen 50
times every second. They can be used for selecting things and even
drawing.

Advantages:

 They are more accurate than touch screens

 They are much smaller and portable than touchscreens
 They are extremely easy to use

Disadvantages:

 There can be lag when the pen is being used to draw

 They only work with CRT (Cathode Ray Tube) monitors
 They are not very accurate for drawing
 The technology is pretty old and outdated
Chapter 3 Storage devices and media
Chapter 3 Storage devices and media

What is a backup?
A backup is another store of data that is stored away from the original
files (this is important when answering exam questions); this is in case
something happens to the original files and the data needs to be
recovered. Files need to be backed up regularly to make sure the
backup is up-to-date. Simple, right?

Why do we backup data?

The general reason we backup data is so we are able to recover it if it
becomes unusable. Here are some examples of how where a backup
may be helpful:

 If something were to happen to the storage device where the originals

are stored (for example: it crashes or gets damaged in a fire or flood)
 One of the originals is accidentally overwritten by another file
 The files somehow get corrupted (maybe via hacking or malware)
 If the files need to be used somewhere other than where the originals
are saved

Serial access:
This method of access is where the user states which record they want
to access in a file, the system then starts at the first record in that file
and searches through all of them (i.e. the first record, then the second,
then the third etc.) until it finds the right record. The obvious problem
with this method of access is that it takes so long to actually access the
record because the system has to search through all these records to
find the right one. It is mainly used on magnetic tape.
Chapter 3 Storage devices and media

When a magnetic tape that uses this method of access needs to be

updated, there are two things that are used that you will need to
know. These are the master file and the transaction file. Don’t worry;
this is a relatively easy thing to understand. The master file is the
original data (so the data that needs to be updated), and the
transaction file is the data that will be used to update the master
file (so basically all the new stuff that has been saved since the master
file was last updated). From these two tapes, a new tape is created
that has all of the original files from the master file as well as all the
new stuff from the transaction file. The only other important thing to
remember is that the master file and the transaction file have to be
sorted in the same way (i.e. have the same key field which is the field
that all the rest of the data in the file is sorted from). If they are not
sorted the same way, then all the data will get messed up.

Direct access:
This method makes use of the key field to work out where the record
should be in the file. This means that it is obviously much faster than
serial access. It also means that when the data is updated, there is no
need for the records to be sorted; the new file just overwrites the old
one.

You should all be familiar with the sizes in which files are stored and
which is biggest and smallest, but in case you need a refresher, here
they are in order of smallest to biggest:

Bytes

Kilobytes (kB): 1000 bytes

Megabytes (MB): 1000000 bytes

Gigabytes (GB): 1000000000 bytes

Terabytes (TB): 1000000000000 bytes

You will not need to know the sizes in bytes, just the size order
Chapter 3 Storage devices and media

There are three types of storage media that we will cover here

Magnetic storage media:

Pretty self-explanatory, the media makes use of the magnetic
properties of certain materials and uses a special coating that let’s
information be converted to 1s and 0s. There are three main types of
magnetic storage media:

Fixed/internal hard disk drive (HDD):

This is the main storage device that is installed on all computers.
Generally, this data is written to and read from the disk contained in
the drive. This disk also stores what is called the DOS (Disk Operating
System) as well as the system software.

Advantages:

 Fast data transfer rate and access time

 Large memory space

Disadvantages:

 Easily damaged if the computer is not shut down properly; this can lead
to loss of data
 Lots of moving parts
 They can be quite noisy compared to SSDs

Portable hard disk drives:

These are just the same as internal hard disk drives except they are
connected to the computer via USB (Universal Serial Bus) instead of
being built into the computer.
Chapter 3 Storage devices and media

Advantages:

 Fast data transfer rate and access time

 Large memory space
 Can be used to transfer data between computers

Disadvantages:

 Easily damaged if the computer is not shut down properly; this can lead
to loss of data
 They are easily damaged since they are not built into the computer (i.e.
they can be dropped)

Magnetic tapes:
These are thin strips of plastic that are coated in a layer of that makes
it magnetic. The magnetic area can then be used to store data. This
type of storage cannot be used for real-time and online applications
because it is too slow. It is used more in batch and offline processing.

Advantages:

 They are cheaper than hard disks

 They are robust
 They have an extremely large amount of storage space
 Fast data transfer rate

Disadvantages:

 Slow data access times

 Requires a whole new tape to update the data
 Can be affected and corrupted by other magnetic fields (i.e. a strong
magnet)
Chapter 3 Storage devices and media

Optical storage media:

CD/DVD disks:
The way a CD/DVD works is that the disk has small grooves in the
surface of the disk where data is written to and read from. A red laser
is used to read and write the data.

There are 4 types of CD/DVD:

CD-ROM and DVD-ROM:

The fact that the disks are ROM (Read Only Memory) means that the
data on the disks can only be read, not written to. These are the kinds
of CD/DVD that are used in music albums or movies. You cannot buy a
movie on DVD and then go and add new files to the disk.

Advantages:

 They can hold more data than a floppy disk

 They are cheaper than hard disks

Disadvantages:

 They have a slower data transfer rate/access time than hard disks
 Less robust than hard disks (this goes for all types of CD/DVD)

CD-R and DVD-R:

These are blank disks that can be written to once only. After is has been
written to, the disk becomes a CD ROM or DVD ROM. The disks are
written to by “burning” them with a laser. The laser produces heated
and unheated spots on the disk that can be distinguished by a laser
beam and read from.

Advantages:

 They are cheaper than RW disks

 Data is protected after the disk is burned (cannot be altered
afterwards)
Chapter 3 Storage devices and media

Disadvantages:

 If something is wrong with the data during or after the burning

process, the disk has to be thrown away and a whole new disk has to be
made
 Some devices can’t read CD-R/DVD-R disks

CD-RW and DVD-RW:

In the case of these disks, the RW stands for “re writable”. This means
that even once the disks have been written to, they can then be
written to again and again afterwards.

Advantages:

 They can be written to multiple times

 They can save multiple different file formats each time

Disadvantages:

 They are more expensive than CD-R and DVD-R

DVD-RAM:
DVD RAM basically performs the same task as DVD-RW, but better.
They can be re-written to over 100000 times. They are great for
archiving files since the disk can survive for so long. They work a little
differently as instead of making heated and unheated areas, the laser
changes the physical properties of parts of the disk, turning them from
shiny to dull.

Advantages:

 Extremely long life (upwards of 30 years)

 They can be re-written to over 100000 times as opposed to the 1000
times that RW provides
 Fast data access times
 No need to throw away the disk if something goes wrong
 Large storage capacity
 Can read data to the disk and data can be read form the disk at the
same time
Chapter 3 Storage devices and media

Disadvantages:

 Less compatible with devices as DVD-R and DVD-RW

 More expensive

Blu-ray disks:
These disks are read by a blue laser (I know. Mind-blowing, right?)
which allows the grooves in the disk to be a lot smaller so that the disk
can store more data. This is why Blu-ray movies are higher definition
than DVD movies, because they have the capacity to hold the larger
file.

Advantages:

 Large storage capacity

 Fast data transfer rate
 Fast data access speed
 Have a built-in encryption system that prevents piracy and copyright
infringement

Disadvantages:

 More expensive than normal CD/DVDs

 There can sometimes be problems with the encryption system

Solid State Drives (SSDs):

These are taking over from HDDs because of this reason. They are more
reliable because they save data using electrons instead of magnetism.

Advantages:

 Since there are no moving parts, there is less risk of something going
wrong
 They are lighter than HDDs
 HDDs have to get the disk to a certain speed to work, this is not a
problem for SSDs
 They consume less power than HDDs
 They have a faster data access time than HDDs
Chapter 3 Storage devices and media

The main disadvantage is that they can’t take as many write operations
as HDDs

Memory sticks (pen drives):

These are a smaller way of storage and carrying data; thus their main
advantage is that they are extremely small and portable. They can be
used to transfer data between computers, and, more recently, they are
used as a form of piracy protection (the memory stick or
dongle contains a validation key that would have to be broken before
the software can be accessed).

Advantages:

 Extremely small and portable

 Robust
 Compatible with most computers
 Not affected by magnetic fields like magnetic tape

Disadvantages:

 No way of protecting the data that is saved on the memory stick

 They are easy to lose since they are small
 If the memory stick is removed without ejecting first, the data can
become corrupted

Flash memory cards:

A micro-SD and its adapter that makes it the same size as a regular
flash card

These are the smallest form of solid state memory (especially with
micro-SD cards). They are mainly used in digital cameras and mobile
phones because of their size.

Advantages:

 Extremely small and easily removable

 Robust
Chapter 3 Storage devices and media

Disadvantages:

 Relatively expensive
 Can only be read from or written to a certain number of types
 Smaller storage space than HDDs