Information representation
Magnitude Prefixes
Binary Prefix
Value
Denary Prefix
Value
Kibi (Ki)
Mebi (Mi)
Gibi (Gi)
Tebi (Ti)
1024 bytes
1024 KiB
1024 MiB
1024 GiB
Kilo (k)
Mega (M)
Giga (G)
Tera (T)
1000 bytes
1000 kb
1000 Mb
1000 Gb
Binary Coded Decimal (BCD)
In a BCD each character in a number is represented by a 4-bit binary number
such as 8 is 1000 and 19 is 00011001. If a character is greater than 9 it cannot
be represented in BCD.
 Used to represent numbers in calculators and counters
 It allows you to accurately measure fractions
 You can electronically code decimal numbers
Hexadecimal
Base 16 from 0-9 to A-F
 Used in MAC and IP Addresses
 Used to represent colors in HTML
 Used in error messages and memory dumps
Character Sets
The characters that a computer can use such as lowercase and uppercase
letters, numbers, and symbols. Each character set has a unique code for each
symbol.
 ASCII
 Extended ASCII
 Unicode
American Standard Code for Information Interchange
Contains 128 characters only from the English language. 7 bit
Extended ASCII
Contains 256 characters from most European languages including English. 8 bit
Unicode
Contains over 10,000 characters from a variety of languages and is the current
standard. Up to 32 bit
Bitmap Images
A canvas filled with pixels that together represent an object
 Pixelates when enlarged
 Large file size
Pixel
The smallest unit of area in an image representing a single color
File Header
Data about the image i.e.;




Image size
Image resolution
Color depth
Number of colors
Image Resolution
Number of pixels per unit area of an image. Higher values increase file size
Screen Resolution
Number of pixels displayed by a screen at a time
Bit Depth / Color Depth
The number of bits used to represent each color i.e.; 4-bit color means 4 bits
so 16 colors because 24 = 16
Higher values increase file size.
“Image Size = Image Resolution x Color Depth”
Lossy image compression can be done by;
 Reducing bit depth which means fewer bits are used to store each pixel
in an image
 Reducing color palette which means less colors and therefore less bits
per pixel
 Reducing image resolution which means fewer pixels per unit area so
less space is needed
Lossless image compression can be done by;
 Run length encoding (RLE) will look for series of consecutive pixels that
store the same color and will index the color and the number of times it
occurs
Vector Images
A series of geometric shapes made with mathematical formulas and their
properties often used for logos that cannot be compressed
 Can be scaled without losing quality as it gets recalculated
 Has a relatively small file size as it stores equations not pixels
Drawing List
A list of shapes involved in a vector image i.e.; triangle, R, line
Drawing Object
An individual shape defined using math in a vector
Property
Data about the drawing object




Line Color
Line width
Fill Color
Shape
Sounds
The frequency/amplitude of the sound are recorded at regular intervals and
are then converted into a histogram when the time comes to replay the
sounds.
Sampling
The process of recording the amplitude and frequency of sound at regular
intervals
Sampling Rate
The number of samples that are taken per unit time. Larger value means more
accurate sound but higher file size as more samples are taken.
Sampling Resolution
The number of bits used to store each sample. Larger values mean more
accurate reconstruction of sound but higher file size as more bits are used to
store the sound.
“Sound Size = Sampling Rate x Sampling Resolution x Time”
Analogue Data
Continuous real-world data
Digital Data
Discrete electrical data
Compression
The act of reducing the size of a file
 To reduce transfer time
 Save bandwidth
 Save storage space
There are 2 types of compression techniques;
 Lossy
 Lossless
Lossy
File size compression where original data is lost and cannot be recovered
 Creates a much smaller file size than lossless
 Useful when significant size reduction is needed
 Significant loss in quality
Lossless
File size compression where original data is not lost and can be recovered
 Maintains quality
 Useful when all original data needs to be recovered
Communication
Networks
Devices in a network are inter-connected and communicate between each
other
 You can easily transfer data like files between devices
 Devices can share resources such as hardware like printers or same
software
 You can store data in drives connected to the network
There are two main types of networks
 Local Area Network
 Wider Area Network
Geographical Region
Ownership
Medium
Speed
Congestion
LAN
Small
Private
Wi-Fi, Copper, Coaxial
High
Low
WAN
Large
Public / Private
PSTN or satellites
Low
High
There are two types of models between computers on a network
 Client-Server
 Peer-to-Peer
Client-Server
In a client-server model the server stores all the data and performs the tasks
requested by the client. The client computer sends requests to the server
which will return the requested result back to the client. Such as when loading
a webpage. Several requests can be made to the server at a time
Some examples include;
 Sending and receiving emails
 A company storing files on a central server
 Print/file/web/proxy/email server
There are pros and cons to this model
 Increased security as only the server has higher privileges
 Increased performance of individual computers they are not receiving
any requests
 There is central management of data and software so there is always a
backup and each device has consistent software
 Since all operations depend on the main server, if the server is down
then the other devices are too
 It is difficult to scale and relatively expensive
 The speed of the network decreases exponentially based on the number
of devices connected
Thin Client
A thin client provides input to the server and receives an output from the
server
Thick Client
A thick client carries out some processing on its own before/after
sending/receiving data to the server
Peer-to-Peer
In a peer-to-peer network all devices on the network are of equal status. Each
computer has access to all the data and resources of another device therefore
each device is responsible for its own safety.




The initial cost of the setup is very cheap
Each device has complete access to any other device on the network
No dependency on a central server
Reduced security as the device is vulnerable to viruses from other
devices on the network
 Reduced performance as other devices might be attempting to access
the data on this computer
 No central backup of files so if one computer loses the data, they all
might lose access to it
Topologies
The way of connecting devices on a network




Bus
Star
Mesh
Hybrid
Bus
All devices are connected to a central cable
that has terminators at the end. Only one
communication can take place at a time.
Data terminators are needed to prevent a
network crash from data collision
Star
All devices are connected to a central
switch/router via its own route. Hence no
collisions can occur and data can be sent
out simultaneously. Alternatively, you can
use hub instead of switch but its slower.
Mesh
All devices on a network are connected to each
other. The internet itself is an example of mesh
topology.
Hybrid
A combination of topologies used together
Cloud Computing
Applications and services that deliver over the internet. A third party hosts the
data for the user that they can then use. Can exist for public, where it can be
used by anyone online, and private use, where it is made specifically for use by
a company.






Free for small quantities
Can access data from anywhere if you have internet
Likely better security and recovery options
Internet access is required to access it
Long upload and download time limits access to data
No control over security and backups
Transmission Mediums
 Wired
o Twisted Pair / Copper Cable
o Fiber-optic cable
 Wireless
o Radio waves
o Micro waves
o Satellites
Copper Cable
Twisted pair of copper wires that carry data as electrical signals
Fiber Optic
Glass/Plastic cables that rely on total internal reflection in order to transmit
data as light
Speed
Distance
Interference
Security
Durability
Price
Fiber Optic Cable
Fast
Long
Low risk
Safe
Low
High
Copper Cable
Slow
Short; needs repeaters
Higher risk
Less safe
High
Low
Radio Waves
An electromagnetic wave that carries data wirelessly; Wi-Fi
Micro Waves
An electromagnetic wave that is used to communicate with satellites
Satellites
A communication device that orbits the Earth and sends/receives data
Radio Wave
Price
Cheap
Obstacles Other radio waves
Distance
Long
Size
Lower
Micro Wave
Expensive
Physical Objects
Shorter
High
LAN Hardware
Certain hardware is used to support the LAN system;




Switch
Server
Network Interface Card (NIC)
Wireless Network Interface Card (WNIC)
Satellites
Expensive
High risk
Long
High




Wireless Access Point (WAP)
Cables
Bridge
Repeater
Switch
Connects all devices on a network and simultaneously broadcasts information
to those devices
Server
A specialized high-speed computer that handles requests from clients or other
computers on the network
Network Interface Card (NIC)
A hardware component that provides each device with a unique MAC address
so that it can be identified
Wireless Network Interface Card (WNIC)
A hardware component that provides each device with a unique MAC address
so that it can be identified on a wireless network.
It provides an interface by acting as an antenna to a Wi-Fi network. It receives
analogue radio waves, that it decodes and converts into a digital data, and it
sends digital data, that it encrypts and converts into analogue waves, via the
antenna.
It checks incoming transmission to see if they match the device’s IP/MAC
address and ignores them if they are not.
Wireless Access Point (WAP)
Allows devices to connect to the network wirelessly that is usually built into a
router; such as Wi-Fi
Cables
Physical means of sending and receiving data on a network
Bridge
A device that interconnects two or more LANs together and forwards data
packets.
Repeater
A network device that amplifies or regenerates a signal to prevent it from
being lost or corrupting
Router
The router is connected to the switch because it is connected to all devices on
the network or to the server because the server acts as the proxy.
The router has several functions
 Maintain a table of MAC and IP addresses
 Assign private IPs to devices on a network
 Route packets to their destination but does not direct packets to each
device attached to it
 Receive packets
Ethernet
The most common form of wired connection used in LAN and WAN that is
based on Bus topology
Due to this it is possible for data collisions to occur, hence a Carrier Sense
Multiple Access/Collision Detection (CSMA/CD) is used.
A workstation listens to the communication channel, when it receives a
request first it will check if the line is empty, if empty sends data. If a collision
occurs because both devices checked if the line was empty at the same time,
then the workstation will send an abort signal and the data will be sent back.
And a random wait time is assigned to each device before resending.
Speed
Stability
Security
Movement
Cabling
Expandability
Wired
Faster
More Stable
More Secure
Restricted
High
Hard
a
Internet Hardware
 Modem
 Public Switch Telephone Network (PSTN)
 Dedicated Lines
Wireless
Slower
Less Stable
Less Secure
Free
Less
Easy
 Cell phone network
Modem
A device that allows users to connect to the internet via telephone line. It
converts analogue signals into digital signals and vice versa.
Public Service Telephone Network (PSTN)
Full duplex form of communication over wire that passes through circuit
switching centers that remains active during power outages
Dedicated Lines
A permanent connection for communication that is expensive but faster and
more secure/consistent




Faster connections
Improved security
Expensive to set up and maintain
Disruption to line would leave no other options
Cell phone Network
A wireless connection that relies on mobile connection and cell towers that use
radio waves
Bit Streaming
A video is compressed and is then sent as a continuous stream of bits. When it
is downloaded the server sends the data to the buffer which then sends a
continuous steam of data to the user.
Higher bit-rate speed and broadband speed means users can stream the video
faster and with less buffering
There are two methods of bit-streaming;
 Real-time
 On-demand
Real-Time
Real-Time bit streaming is used when watching a live stream of events that are
currently taking place. The event is captured live with a video camera
connected to a computer, and it cannot be paused or rewound
On-demand
On-demand bit streaming is used when watching an event that has taken place
in the past. Existing media are encoded to bit streaming format and uploaded
to a server. It can be paused and rewound
World Wide Web (WWW)
The world wide web is the collection of websites that are available on the
internet. When you access a website, you are using both the internet and the
world wide web because the website is stored on WWW but the internet
provides the necessary infrastructure.
IP Address
The unique address that identifies a device a network and to allow router to
send data from the internet to the device. There are 2 formats for an IP
address;
 IPv4
 IPv6 – Invented because number of IPv4 addresses will run out
Number of Groups
Group Range
Separator
Size
Example
IPv4
4
0-255
.
32-bit
192.168. 1.1
IPv6
8
0-65535
:
64-bit
fe80::d4a8:6435:d2d8:d9f3b11
:: can only show up once in each IPv6
Types of IP Addresses
There are many types of IP addresses;




Public
Private
Static
Dynamic
Public
Assigned by the ISP that is visible to any device on the internet. Must be
unique on the internet.
Only the router has a public IP address, the devices on the network do not as
all data passes through the router. This also protects the device from external
threats
Private
Assigned by the router that is visible to devices on the network. Must be
unique on that specific network.
Static
Remains constant whenever a device connects to the internet. Webpages need
static IP addresses so that the DNS does not need to be updated every time
which can cause delays and errors.
Dynamic
A new IP address is allocated every time a device connects to the internet
Subnetting
The practice of dividing a network into smaller groups.
 Reduces traffic
 More secure
URL
Uniform Resource Locator, an easier way to remember IP Addresses for
websites. Google.com > 152.245.23.001
Domain Name Server (DNS)
When you type a URL it is sent to the DNS. The DNS looks up the URL within a
table and if it finds the corresponding IP Address, it is then returned to the
client. If it cannot find the IP Address, the request is forwarded to a higher
DNS.
Hardware
Primary
Electrons are stored as volatile data in RAM.
Volatile means the data is lost when the voltage is lost (turned off)
 Read Only Memory (ROM)
 Random Access memory (RAM)
Secondary
Non-volatile storage
 Magnetic/Hard Disk Drive (HDD)
 Solid State Drive (SSD)
Read Only Memory (ROM)
Non-volatile, write speed is slow and stores basic information that a device
needs to operate/boot. ROM is used to store information that does not change
or information that needs to be retained even when the device is turned off.
There are 3 types of ROM;
 Programmable ROM (PROM)
 Erasable Programmable ROM (EPROM)
 Electronically Erasable Programmable ROM (EEPROM)
Programmable ROM (PROM)
A ROM chip that is initially empty but can be written to once
Erasable Programmable ROM (EPROM)
A ROM chip that can erased by using a UV light to heat up the circuit and erase
it. Can be overwritten many times. EPROM needs to be completely erased
before overwriting.
Electronically Erasable Programmable ROM (EEPROM)
A ROM chip that can be erased electronically using voltage. It is a type of flash
memory that means it can be rewritten quickly and many times. EEPROM can
be partially erased and overwritten.
Random Access memory (RAM)
Volatile with fast read and write speed that stores the current program in use.
There are 2 types of RAMS;
 Static RAM (SRAM)
 Dynamic RAM (DRAM)
Static RAM (SRAM)
A type of RAM in which data remains constant if power is supplied. It is
commonly used as CPU cache and buffers due to its lower storage capacity.
Transistors are arranged as flip flops. Uses multiple transistors.
Dynamic RAM (DRAM)
A type of RAM that stores each bit on a capacitor and therefore needs to be
constantly refreshed. DRAM is used for personal computers and webservers as
its cheaper. Transistors are arranged as capacitors. Uses a single transistor and
capacitor.
ROM
MBs
False
Slower
Size
Volatility
Speed
RAM
GBs
True
Fast
DRAM
Cheap
Slow
High
Low
High
Price
Access Speed
Power Use
Heat
Size
SRAM
Expensive
Fast
Low
High
Low
Secondary Storage ⇌ DRAM ⇌ RAM ⇌ Microprocessor
Size –
Speed +
Price +
Magnetic/Hard Disk Drive
A hard disk has one or more platters mounted on a spindle. The platter is
divided into concentric tracks and sectors. It is spun at a very fast speed. A read
and write head is mounted on an arm above the surface. The data is encoded
as magnetic patterns.




Cheaper than SSD
Longer life span
Moving parts so it can be loud
Slower
Solid State Drive
Blocks of transistors are arranged in a grid with two transistors at each
intersection; the floating gate and the control gate. Memory cells stores 0s and
1s. Movement of electrons is controlled for read and write operations.
 Faster
 No moving parts
 Shorter life span
 Expensive
Buffer
A temporary storage usually in the RAM that is used due to speed
incompatibility between devices. Such as a video buffer when steaming videos.
Embedded Systems
An integrated system with microprocessor within a larger system that
performs one specific task.







Compact and fast
Consumes less power and is very reliable
Cheap
Tedious and difficult to upgrade
Time needed to maintain it
Hard to backup
Not easily changed by device’s owner
Input Output Devices







Laser Printer
3D Printer
Microphone
Speaker
Optical Disc Reader/Writer
Touch Screen
Virtual Reality Headset
Laser Printer
The drum has an initial charge. As it rotates, a laser bounces back and forth
across the drum in certain areas to remove the charge.
The drum is coated with a charged toner which sticks to the charged area. As a
piece of electrostatically charged paper is rolled in, the toner sticks to it and
the pattern is transferred.
The ink is melted so that it continues to stick to the paper even after charge is
removed by passing it into the fuser. Lastly the excess toner is collected.
3D Printer
A 3D design is made using CAD. The design is split into layers that are
transmitted one by one to the printer.
The printer head can move in all cardinal directions squirting out material. This
is repeated for every layer. After that it needs to be cured; either by removing
excess material or letting the material dry/harden.
Microphone
As sound is passed into the diaphragm is vibrates. The diaphragm is connected
to a circuit where the vibrations cause a change in the electrical signal. The
analogue signal is then converted into a digital signal by an ADC.
Speaker
The digital signal is converted by a DAC. The analogue signal is then sent as
current to a speaker. The current passes through the coil creating an
electromagnet, which is attached to the diaphragm.
Changes in the sound affect the direction of the current. The electromagnet is
constantly being attracted/repelled by a permanent magnet causing the
diaphragm to vibrate and produce sound.
Optical Disc Reader/Writer
An optical disc is spun on a spiral track, as it spins the pits and lands are read
by a laser. The pits and bumps reflect light differently. The surface of the disc
is coated in a reflective metal layer. The lens helps focus the laser onto the
disc. The difference in the reflection of a pit and land is read as 0s and 1s
Touch Screen
There are two types of touch screens;
 Resistive
 Capacitive
Resistive
Two charged plates. When you press on the screen the two layers connect and
complete a circuit. Point of contact is registered and the coordinates are used
to calculate position.
Capacitive
A conductive layer stores charge. When touched charge is transferred to the
finger. Sensors at the corner of the screen detect changes and the point of
contact is registered and the coordinates are used to calculate position.
Virtual Reality Headset
A headset contains two eye pieces which are fed images from a controlling
system which when looked through simulates being in a 3D environment.
When the user moves their head or uses the controlling device they can move
and look around in the environment.
Sensors
Sensors are input devices that provide data based on real-word data.




Temperature
Infrared
Pressure
Sound
Actuators are used in tandem with sensors, they provide the output.
When using sensors, there are two main types of systems;
 Monitoring
 Controlling
Monitoring
A system in which the sensors are used to detect changes, they cannot resolve
the issue itself. For example, if a temperature gets too high, it will turn on a red
light. Human intervention is needed
Controlling
A system in which the sensors are used to detect changes and resolve the
issue. For example, if a temperature gets too high, it will turn on the air
conditioning. No human intervention is needed.
Logic Gates
Not
A
0
1
A NOT
1
0
OR
AB
00
01
10
11
X
0
1
1
1
AB
00
01
10
11
X
0
0
0
1
AB
00
01
10
11
X
1
0
0
0
AND
NOR
NAND
AB
00
01
10
11
X
1
1
1
0
AB
00
01
10
11
X
0
1
1
0
XOR
Logic Circuit
Logic Expression
(A+B) ⊕ (A+B)
Processor Fundamentals
Fetch-Execute Cycle
1.
2.
3.
4.
5.
The contents of the PC are copied to the MAR
The PC is incremented by 1
The MAR fetches the data at the given address and loads it into the MDR
The contents of the MDR are copied to the CIR
The instructions are decoded by the CPU and executed by the CIR and
the cycle repeats
Register Notation
MAR <- [PC]
PC <- [PC] +1
MDR <- [[MAR]]
CIR <- [MDR]
Registers
A register is the temporary storage of data that needs to be or has been
processed. There are many registers in a computer such as;







Program Counter (PC)
Memory Data Register (MDR)
Memory Address Register (MAR)
Current Instruction Register (CIR)
Index Register (IX)
Accumulator (ACC)
Status Register (SR)
Program Counter (PC)
Stores the address of the next instruction to be fetched
Memory Data Register (MDR)
Stores the data that has been received/transmitted from/to CIR/memory
Memory Address Register (MAR)
Stores the address where the data that needs to be fetched is located and
sends to MDR
Current Instruction Register (CIR)
Stores the data received from the MDR
Index Register (IX)
Stores a value that is used to calculate an address
Accumulator (ACC)
Stores the values temporarily after an execution of instruction by ALU
Status Register (SR)
Contains independent bits/flags where each flag is set based on an event
Arithmetic Logic Unit (ALU)
Part of the processor that carries out arithmetic and logical operations like
input and output
Control Unit (CU)
Sends and receives signals to control operations like input and output. And
helps coordinate actions of different components.
Immediate Access Store (IAS)
The components that directly addressed by the processor
System Clock
Generates the timing signals that synchronize the components on the
motherboard
Number of Cores
Each core processes one instruction per clock pulse so more cores means more
than one instruction can be processed
Clock Speed
Each instruction is executed on a single clock pulse so the faster the clock
speed the more instructions that can be executed per second
Bus Width
The number of directly addressable memory locations to transfer data
between
Cache
Stores frequently/recently used information so that it can be quickly accessed
Universal Serial Bus (USB)
Fast data transfer for large files like videos and supports plug and play so no
need to install drivers
Video Graphics Array (VGA)
Transfers high resolution image display without sound
High Definition Multimedia Interface (HDMI)
Transmits high quality videos and sound
Data Bus
Carries data between processor and memory, it is bidirectional
Control Bus
Transmits control signals between CU and other components, it is bidirectional
Address Bus
Carries addresses from MAR to memory location, it is unidirectional
Interrupts
An interrupt is a signal from a device telling the processor that its attention is
needed




Printer is out of paper
Runtime error
User interaction
Input or output request
At the start and end of every fetch and execute cycle the processor checks for
interrupts, if an interrupt is found it identifies the source and priority.
If lower priority than current task it continues the cycle else if it is higher
priority than the current task, the current task is pushed to stack and the
Interrupt Service Routine (ISR) is called.
After the interrupt is serviced, it checks to make sure there are no interrupts of
high priority that need to be serviced then the task is pulled from the stack and
the fetch execute cycle continues.
Assembly Language
A low-level language that is used to directly instruct the registers and
microprocessors. There are 5 categories of instructions.





Data Movement
Input and Output
Arithmetic Operations
Conditional and Unconditional Jumps
Comparison
Data Movement
LDM <#n/Bn/&n> // Loaded to ACC
LDD <address> // Contents of address loaded to ACC
LDI <address> // Contents of address of address loaded to
ACC
LDX <address> // Content of IX added to address to form a
new address and data from there is loaded to ACC
LDR <#n/Bn/&n> // Loaded to IX
MOV <register> // Move contents of ACC to <register>
STO <address> // Store contents of ACC at <address>
Input and Output
IN <> // Store the ASCII value of the char in the ACC
OUT <> // Output the character based on the ASCII value in
the ACC
Arithmetic Operations
ADD <#n/Bn/&n> // Add to ACC
SUB <#n/Bn/&n> // Subtracts from ACC
INC <register> // Increment register
DEC <register> // Decrement register
Conditional and Unconditional Jumps
JMP <address> // Jump to given address
JPE <address> // Jump if true; after comparison
JPN <address> // Jump if false; after comparison
Comparison
CMP <#n/Bn/&n> // Checks if ACC is equal to value
CMI <address> // Check if contents of address of the
address is equal to ACC
 # Represents a decimal number
 B Represents a binary number
 & Represents a hexadecimal number
Immediate
The operand is the value used in the instruction
Direct
The value of the address is used in the instruction
Indirect
The operand stores an address that points to another address that stores the
data
Indexed
The operand is added to the index and the data at the address is used
Relative
The operand is added to a set address to calculate where to read value from;
offsets. It is used to allow for relocatable code as all addresses are base +
offset.
Assembler
The assembler runs in two phases. In the first phase it reads the instructions,
when it sees a symbolic address, it checks if it is in the symbol table, if it is not
then it is added to the table. If it is already in the table, it checks if the absolute
address is known, if yes, it is entered else it is marked as unknown.
During the first run it also removes comments and expands macros. During the
second run the code is executed/generation of object code. Code is read in
both runs.
Logical Shift
 LogicalShiftLeft (LSL) multiples the number by 2 to the power n
 LogicalShiftReft (LSR) divides the number by 2 to the power n
LSR <#n> // Move towards right; empty spaces are 0s
LSL <#n> // Move towards left; empty spaces are 0s
Arithmetic Shift
Works like the logical shift except that most significant bit stays the same, i.e.,
the number stays positive/negative.
Absolute Address
A numerical address that points directly to a memory location
Symbolic Address
A word or symbol that represents a memory location
System Software
Operating System
An operating system is a piece of system software that facilitates
communication between the user and the hardware
Need
 To provide a means of communication between hardware and user
 To provide an environment for the execution of software
 To manage system resources
Tasks
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Memory Management
File Management
Security Management
Hardware/Input Output/Peripheral Management
Process Management
Error detection and Management
User Interface
Memory Management
 Allocates memory to processes when they need to run
 Releases memory when a process stops so that it can be recycled and
reused
 Makes use of virtual memory when the main memory is under struggle
due to a small capacity
 Controls movement of data to/from RAM
 Memory protection to make sure that 2 programs do not use the space
File Management
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Allocates space to a given file
Allows use of copy, paste, cut, delete, open, close and create.
Maintains and creates directory structure
Provides file naming conventions like it cannot contain illegal characters
like ‘/’
 Provides access rights to prevent certain users on the device from
accessing the files
Security Management
 Performs automatic backups in case of accidental deletions
 Sets up user accounts and implements access rights per user like
‘Administrator’
 Provides a system restore when needed by the user
 Authenticates the username and passwords of the different accounts on
the device
Hardware Management
 Automatically installs necessary drivers when the device is plugged in
 Handles the interrupts and signals sent to/from the device including the
device buffer
 Sends control signals in order to manipulate the device, such as start
printing a document
Process Management
 Manages the scheduling of different tasks in order to allow for multitasking
 Prevents interferences between different processes such as over
resources
 Manages the resources which the process requires
Error Detection Management
 Handles interrupts
 Provides safe mode boot up in case of a major error
 Provides error diagnostic messages and reports on the health of the
system
 Saves system restore points
User Interface
 Allows the user to communicate with the hardware by providing a CLI or
GUI
 Provides facility for the user to input and output data to/from the
hardware
Utility Software
Software that is installed by default on every computer just as a virus checker.
A photo editor is not an example of utility software
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Disk Formatter
Virus Checker
Defragmentation Software
Disk Repair and Analysis Software
File Compression
Backup software
Disk Formatter
The disk formatter prepares the hard disk for its initial use by creating logical
partitions usually on a previously used disk.
Virus Checker
The virus checker scans the files stored on the system and files that newly
enter the system for malicious code. It does this on a regular schedule. If a file
is found it can be quarantined and deleted.
Defragmentation Software
Reorganizes the individual files on the system to ensure that they are stored in
contiguous blocks to speed up access times.
Disk Repair and Analysis Software
Scans the disk for corrupt/bad sectors and marks them as unusable. It will
resolve any errors and provide reports to the user
File Compression
Reduces the size of the file to optimize storage space by using an algorithm
such as RLE, which can be lossy or lossless.
Backup Software
Creates copies of the content of the disk usually on schedule. Allows the user
to decide what data is stored and when needed allows the user to restore the
saved data
Program Libraries
A collection of pre-written code that can be linked to the main program to
perform complex tasks
 Saves time as you can refer to the library instead of writing the code
yourself
 Allows you to perform complex tasks without needing to understand
how it works
 It has been thoroughly tested so you can use it without error checking
Dynamic Link Library
A collection of self-contained programs that have already been compiled.
These are linked to the main program for execution
Library program’s code is separate from the .exe file which means the library
file is loaded at run time when it is needed
A DLL file can be used by multiple programs at the same time and it can be
automatically be updated
 Only loaded when needed so that means the executable’s size can be
smaller
 Changes made to the DLL are separate from the executable so it does
not need to be recompiled and it can be updated automatically
 Saves time as you can refer to the library instead of writing the code
yourself
 Allows you to perform complex tasks without needing to understand
how it works
 It has been thoroughly tested so you can use it without error checking
 Executable will not work if the DLL is corrupt
 External changes to the DLL could cause the executable to stop working
 The DLL needs to be present for the executable to work
Translator
A software that is used to convert higher level programming languages to a
different form, usually machine code
 Compiler
 Interpreter
 Assembler
Interpreter
An interpreter requires the source code to be present when it reads line by line
and stops whenever there is an error.
 Allows for easier debugging as the errors are outputted one at a time
whenever they are encountered
Compiler
It reads the entire program and reports all errors in the end.
 Produces an executable file allowing for redistribution without the
source
Some high-level languages like Java are partially interpreted and partially
compiled.
 Programs can be interpreted on different platforms
 Extra CPU resources may be needed as program needs to be interpreted
on the user’s device which may run slowly
Integrated Development Environment (IDE)
An IDE is a software that helps programmers work more efficiently. They come
bundled with many features
 Context sensitive prompts that auto complete what you are typing based
on what has been typed out
 Dynamic syntax checking which highlights all syntax errors for you
 Pretty print which uses colors and automatic indentation to make the
code more presentable
 Breakpoints which allow you to pause the program at certain points in
execution to ensure line by line that everything is working
 Report window which outputs the contents of variables and data
structures
 Single stepping which executes one line of code and stops
Security, privacy, and data integrity
Data Security
Prevents accidental or malicious data loss
 Firewall
 Access Rights
 Passwords / Biometrics / 2FA
Data Privacy
Prevents unauthorized access to data
Security Measures
It is important to protect both data and the computer system
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User Accounts
Authentication
Digital Signature
Firewall
Anti-virus
Encryption
User Accounts
Allows the administrator to specify different permissions for the users such as
read and write access so that unauthorized actions cannot be carried out.
Each user has an account with a password and username which helps prevent
access to the system without a valid username and password
Authentication
Using a strong password with a unique combination of letters, numbers and
symbols makes it hard to crack. Additionally using biometric data such as face
id or fingerprint makes it even more difficult. 2 Factor/Step verification using
an external device can help make sure no one access your account while you
are away.
Digital Signature
Encrypted data that is electronically attached to files to verify it is from a
trusted source
A digital signature is created by producing a digest by putting the content
through a hashing algorithm. The digest is encrypted with the sender’s private
key and can only be decrypted by using their public key.
Firewall
Monitors incoming and outgoing traffic against a given criteria and will block
anything suspicious that does not meet the requirement. It maintains blacklist
of Ip address. It also has log of all traffic
Anti-Virus
It scans the files stored on the system and files that newly enter the system for
malicious code. It does this on a regular schedule. If a file is found it can be
quarantined and deleted.
Encryption
It is the process of converting a given input into an unreadable format using a
key. If the file is accessed without the key its useless. A decryption key is
needed to unscramble the data
Security Threats
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Virus
Spyware
Hackers
Phishing
Pharming
Virus
A piece of malicious code that self-replicates itself with the intention of
harming a computer system by corrupting data
Spyware
A piece of malicious software installed on the victim’s device that records
keypresses and relays them to a third party without the user’s knowledge
Hackers
Unauthorized access to the victim’s device with malicious intent such as to
steal sensitive information
Phishing
The user is redirected to a fake link usually through email that attempts to gain
sensitive personal information
Pharming
The user is redirected to a fake website that appears legitimate to gain access
to sensitive information
Data integrity
Ensures data is accurate and up to date
 Validation
 Verification
Data Validation
A method of checking if the data entered is valid but not accurate
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Range Check
Format Check
Length Check
Prescence Check
Existence Check
Check digit
Range Check
Data must be between a given range i.e.; 1-100
Format Check
Data must match a given format i.e.; DD/MM/YY
Length Check
Data must match a given length i.e.; have 25 characters or below
Prescence Check
Data must not be left empty
Existence check
Data must exist i.e.; if you are inputting a file name that file needs to exist
Check Digit
An arithmetic operation is carried out on the given input and the data must
match the answer i.e.; international standard book number
Data Verification
A method of checking that data is the same as the original during entry and
transfer
 Entry
o Visual check / Proofreading
o Double entry
 Transfer
o Checksum
o Parity Check
Visual Check / Proofreading
Data must be manually compared by the user to ensure it is correct
Double Entry
Data must be entered twice and then both inputs are compared to each other
Checksum
Data entered is passed through an algorithm to produce the checksum, the
checksum is then sent along with the data. The checksum is recalculated and
compared
Parity Check
Each row and column have even/odd parity, an even/odd number of 1 bit,
depending on what is chosen. An additional parity byte is sent to ensure there
is parity horizontally and vertically. The intersection of the row and column
where the parity is broken is the error bit.
Parity check fails when multiple bits transmitted incorrectly as they might
cancel out.
Ethics and Ownership
Copyright
It is the formal/legal right to ownership and protection of intellectual property.
It allows you legal action against those who misuse it and restrict its usage.
Ethical Body
A group of people entrusted with maintaining operations of a legitimate
occupational business.
 Provide ethical guidelines so the employee does not need to make
decisions on his own
 Provide help and support such as legal advice when needed
 Provide training courses to ensure the employee’s skills are always
polished
IEEE Code of Ethics
 Public – Software engineers shall act consistently with the public
interest.
 Client and Employer – Software engineers shall act in a manner that is in
the best interests of their client and employer consistent with the public
interest.
 Product – Software engineers shall ensure that their products and
related modifications meet the highest professional standards possible.
 Judgement – Software engineers shall maintain integrity and
independence in their professional judgment.
 Management – Software engineering managers and leaders shall
subscribe to and promote an ethical approach to the management of
software development and maintenance.
 Profession – Software engineers shall advance the integrity and
reputation of the profession consistent with the public interest.
 Colleagues – Software engineers shall be fair to and supportive of their
colleagues.
 Self – Software engineers shall participate in lifelong learning regarding
the practice of their profession and shall promote an ethical approach to
the practice of the profession.
Software License
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Free Software
Opensource
Shareware
Commercial
Free Software
The source code comes with the software. If the software is modified, the
edited source code must be released under the same conditions as the original
software.
Opensource
Software is released with the source code. Users can edit and redistribute it.
Usually, free.
 Allows users to edit code
 Allows users to fix errors
 Allow for collaboration
Shareware
Software that needs to be bought on a subscription model, usually free for a
limited amount of time. You may re-distribute. Do not have access to the
source code
Commercial
Software that needs to be purchased. A key is needed to install it. Source code
is not provided. No unauthorized redistribution
 Can earn money by charging a fee
 Allows program to be copyrighted
 Prevents illegal access and changes to the program
Artificial Intelligence
Artificial intelligence can be trained to perform tasks much faster than humans.
It can be trained by putting it through that situation multiples times and
passing in different arguments based on the situation allowing the processor to
decide accordingly. It can store the results of choices and determine if they are
helpful and analyze the helpful ones and repeat them in order to succeed.
Databases
Item
A single entry
Fields/Attributes
The headers of the table
Tuples/Record
Combination of interrelated fields
Table
A collection of records
Databases
A collection of tables
Data Dictionary
Stores metadata about the database like relationships, primary and foreign
keys
Logical Scheme
The overview of the database structure using methods like an ER diagram
Primary Key
A field that is unique for every record, it cannot be repeated or null like an ID
Composite Key
When multiple fields are used to make a primary key
Secondary Key
A candidate key but not a primary key.
An alternative field to the primary key when primary key is unknown
Foreign Key
A field which is common between two tables and hence is used to link them
Candidate Key
A field which has the potential to be a primary key but is not as only one
primary key is needed.
First Normal Form
Figuring out key fields and their dependencies from the flat file to create
multiple tables to avoid data repetition. Contains no data repetition.
Second Normal Form
Creating relationships between tables while avoiding partial dependencies and
many-to-many relationships, an extra table might be needed. Contains no
partial dependencies.
Third Normal Form
Figuring out non key fields and their dependencies to create an extra table and
avoid data repetition. Contains no transitive dependencies.
Flat File
The file that keeps the data of all entities
Master File
The file which holds the basic data of an entity that does not need to be
repeated
Transactional File
The file which keeps data of all entities during a transactional period which
may change during the next transactional period
Partial Dependency
When a field only depends on one part of the composite primary key
Transitive Dependency
When a value does not depend on primary key and depends on another value
instead like in TABLE(PetID, Owner, Number) number depends on Owner not
PetID
Referential Integrity
Referential Integrity is making sure that tables do not try to refer to values that
do not exist. A primary key cannot be updated or deleted unless all dependent
values are deleted/updated. Every foreign key needs to have a corresponding
primary key value with the same data type.
ERD
Entity relationship diagrams
One to One
One to Many
Many to Many
Primary to primary
Primary to non-primary
Non-primary to nonprimary
SQL
Structured Query Language
DDL
Data Definition Language
DML
Data Manipulation Language
CREATE DATABASE Name
CREATE TABLE Student (ID INT,
Name VARCHAR(25),
Address TEXT,
Number INT,
Birthday DATE,
PRIMARY KEY (ID));
ALTER TABLE Student ADD PRIMARY KEY (ID);
ALTER TABLE Student ADD PRIMARY KEY (ID, ID2);
ALTER TABLE Student ADD FOREIGN KEY (ID) REFERENCES
Grades(ID);
ALTER TABLE Student ADD COLUMN Class VARCHAR(2);
ALTER TABLE Student DROP Class;
INSERT INTO Student VALUES(1, “Ali”, “ABC”, 123,
1/1/1);
INSERT INTO Student (ID, Name, Birthday) VALUES(2,
“Asim”, 2/2/2)
DELETE FROM Student WHERE ID = 2;
UPDATE Student SET Number = 456 WHERE ID = 2;
SELECT ID, Birthday, Name FROM Student
SELECT Name FROM Student WHERE Name LIKE “123*”
SELECT Name, Rating FROM Movie INNER JOIN Timings ON
Movie.ID = Timings.ID WHERE Movie.Name = “Monster”;
SELECT ID, Birthday FROM Student ORDER BY Name
ASC/DESC GROUP BY Class;
SELECT COUNT(Name) FROM Student;
SELECT SUM(ID) FROM Student;
SELECT AVG(Percentage) FROM Student;
File Based Approach
 There is more data redundancy because the same data is being stored in
multiple different places
 Worse data integrity because duplicate data might be stored differently
in certain places
 Lack of privacy as all users have equal access to it
 Difficult to perform complex searches as a new program must be written
each time
Relational Database
 Multiple tables are linked together which improves data integrity and
reduces data redundancy
 Complex queries can easily be used to find very specific data
 User permissions can be setup to improve security and data privacy by
preventing them from seeing data they should not
Database Management System
Serves as the interface between the user and the database
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Developer Interface to create interactive features and generate reports
Query processor to design new SQL queries
Password and biometrics to protect against unauthorized access
User accounts to restrict what a user can do (read/write)
Automatic backups in case of data loss
Encryption to make data incomprehensible to people