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○ Takes less space than binary ○ Easier to read and write ○ Easier to debug ○ Used in: MAC addresses, IPv6, HTML color codes, assembly language, error codes ● Denary : Base 10 system (0-9) ○ Easy for humans to read ○ Less range than hexadecimal
Overflow Error
● Occurs when a number larger than a register can store is generated ● Example: Value greater than 255 in an 8-bit register ● Computer has a predefined limit for storage; overflow is when a value outside this limit is generated
Logical Shifts
● Can be left or right ● Left or right most ones are lost and places are filled with 0s ● Most or least significant bits are lost ● Each left shift means multiply by 2 ● Each right shift means divide by 2
Converting Text to Binary
● Done using a character set (ASCII or Unicode) ● Each character has a unique binary value ● ASCII represents up to 8-bit binary numbers ● Unicode is a newer version with greater range (16-bit) ● Unicode requires more bits per character
Converting Images to Binary
● Image is made of pixels ● Each pixel stores one colour ● Image has a set number of pixels wide by pixels high ● Each colour has a unique binary value/colour code ● The colour/binary value of each pixel is stored in sequence ● File contains metadata to identify how the file should be displayed ● Metadata can include colour depth/resolution ● Image resolution : The dimensions of an image (pixels wide × pixels high) ● Colour depth : Number of bits used to represent each colour
● File size increases with higher resolution and colour depth
Converting Sound to Binary
● Sound sampling is done to record sound waves at set time intervals ● Sample rate: Number of samples taken per second ● Sample resolution: Number of bits per sample (defines amplitude variations) ● Determines how quiet/loud sounds can be recorded (e.g., 16-bit) ● Loudness and pitch depend on sample resolution
File Compression
Benefits of Compression
● Reduces storage/memory space ● Sending/receiving email accounts may have restricted file size for attachments ● Reduces time taken to transmit/upload/download ● Reduces bandwidth needed ● Reduces data usage (for mobile clients)
Lossy Compression
● Permanently removes data deemed unnecessary ● Suitable for images and sound ● For images: removes colors humans can't distinguish, reduces color depth and resolution ● For sound: removes sounds humans can't hear, reduces sample resolution and rate ● Not suitable for text files as it will damage/corrupt the file ● Quality of images will be reduced
Lossless Compression
● Uses compression algorithms without permanently removing data ● Common method: RLE (Run Length Encoding) ● Identifies repeating patterns/words/characters/phrases ● Indexes patterns with their number of occurrences and position ● Suitable for text files
2. Data Transmission
Packets
● Small units of data ● Structure:
Error Detection Methods
Parity Check
● Parity can be set to odd or even ● Sender and receiver agree on parity to use ● Data is split into bytes/blocks of 7 bytes ● Sender counts the number of 1s/0s in each group/byte ● Each group/byte is assigned a parity bit to match the parity (odd/even) ● Receiving device recounts the number of 1s/0s in each group/byte ● Compares to parity used; if it does not match, an error is reported ● (In block check) the location of errors can be identified at the intersection ● Limitation: If two bits are corrupted, parity check might not detect the error
Checksum
● Value is calculated from the data using an algorithm ● Value is transmitted with the data ● Value is recalculated by receiver using the same algorithm ● If checksum values are different, there is an error
Echo Check
● Involves comparison of data ● Sending device sends the data ● Receiving device retransmits the data back to sender ● Sending device compares the returned data to what it sent ● If same data, no error; else, error ● Slow method and errors can occur during retransmission
Automatic Repeat Request (ARQ)
● Uses acknowledgment and timeout ● Sender starts a timer when data is transmitted ● Receiver uses an error checking method ● If no error detected, a positive acknowledgment is returned ● If error detected, negative acknowledgment is returned ● If sender gets no acknowledgment within the set time, it resends the data
Data Entry Error Detection
Check Digit
● Used to check for errors in data entry ● A check digit value is calculated from data using an algorithm (e.g., ISBN-13) ● Number is stored with data
● When data is entered, value is recalculated ● If same, then it's correct; if not, error in entry ● A type of validation
Encryption
● Done to make data secure ● Data before encryption is plain text ● Encryption key is the algorithm used ● Cipher text is the name after encryption
Symmetric Encryption
● Shared key used to encrypt and decrypt ● Both the sender and receiver know the key ● Used at small scale ● Less secure (easier for hackers to intercept both key and text)
Asymmetric Encryption
● Different keys: public key and private key ● Public key to encrypt the data and private key to decrypt ● Anyone can know the public key but only those intended know the private key ● Two different keys make it more secure ● Used at larger scale
3. Hardware
Input and Output Devices
Input Devices
● Keyboard ● Mouse ● Scanner ● Touch screen ● Microphone ● Camera/webcam
Output Devices
● Monitor/screen ● Printer ● Speakers ● Projector
● Program Counter has the address of next instruction stored (a location in RAM) ● PC sends this address to MAR using address bus ● MAR sends this address to RAM using address bus ● RAM sends the data at that address to MDR using data bus ● MDR sends that data to CIR using data bus in control unit
Decode Stage
● Control Unit decodes using instruction set ● Instruction set: A list of machine code commands that can be processed by the CPU
Execute Stage
● If decoded data needs mathematical processing, it is sent to ALU ● ALU performs arithmetic processes ● Accumulator stores interim data ● CU tells all components to perform their function using the control bus
Factors Affecting CPU Performance
Cores
● A single core contains all components to do one FDE cycle ● One core means one FDE at a time ● Multiple cores enable faster processing and multitasking ● Increased performance as instructions can be processed simultaneously
Clock Speed
● Clock speed determines number of FDE cycles per second ● 1 Hz = 1 FDE per second ● Usually measured in GHz (billions of instructions per second) ● Overclocking can increase speed
Cache
● Data storage in CPU that stores frequently used data/instructions ● Speeds up processing by avoiding repeated memory fetches ● Purpose: To speed up access as it's faster to access than RAM
Sensors in Automated Systems
● Capture different types of data to be processed by the system ● Convert analog data from environment to digital for processing ● Types include: ○ Acoustic: Measures sound
○ Accelerometer: Measures acceleration forces ○ Flow: Measures fluid flow ○ Gas: Measures gas presence and concentration ○ Humidity: Measures moisture levels ○ Infrared: Measures infrared radiation, can show distance ○ Level: Measures fluid levels ○ Light: Measures environmental light ○ Magnetic Field: Measures magnetic fields ○ Moisture: Measures moisture levels
Primary Storage
RAM (Random Access Memory)
● Directly accessible by CPU ● Volatile storage (loses data when power is off) ● Stores data/instructions currently in use ● Contents constantly change ● Can be increased easily ● Used in the FDE cycle ● Stores: ○ Currently running data ○ Currently running instructions ○ Currently running parts of OS
ROM (Read-Only Memory)
● Directly accessible by CPU ● Non-volatile storage (retains data when power is off) ● Stores startup instructions : ○ BIOS ○ Bootstrap/bootloader ○ Firmware ● Contents are fixed and do not change (unless reprogrammed) ● Difficult to alter ● Stores data/instructions that should not change
Cache
● Stores frequently used instructions/data ● Volatile storage (temporary data) ● Faster access than RAM
Secondary Storage
○ Laser is shone at the disk ○ An arm/head moves the laser across the surface ○ Laser burns pits onto the surface ○ Laser reads the pits and lands on the surface ○ Reflected light is captured by a sensor ● Examples: Blu-ray, DVD, CD
Virtual Memory
● Extension of RAM using hard drive space ● Created when RAM is full ● System sends less urgently needed data to virtual memory as "pages" ● Pages are returned to RAM when needed ● Purpose: To run programs when there is insufficient RAM
Cloud Storage
● Collection of servers that store data in remote locations ● Accessed using internet connection ● Benefits: ○ Data accessible from any location (employees can work from anywhere) ○ Hardware owned/maintained by third party (company not responsible) ○ Storage can be easily increased/decreased ○ No need to house hardware (saves space) ○ Automatic backups ● Disadvantages: ○ Internet connection needed/must be stable ○ Employees could be pressured to work outside hours ○ May be less secure ○ Extra fees
Networking Components
NIC (Network Interface Card)
● Component necessary for computer to access a network ● Each NIC given a MAC address during manufacturing
MAC Address (Media Access Control)
● First part is manufacturer ID ● Second part is serial number ● Each part has 3 pairs of numbers (6 pairs of 2 digits total) ● Numbers between 00 and FF ● Separated by colons (:)
● 6 bytes long (48 bits) ● Represented in hexadecimal ● Physical address that uniquely identifies a device ● Doesn't change
IP Address (Internet Protocol)
● Allocated by router ● Functions: ○ Uniquely identifies a device on a network ○ Identifies global address on the internet ○ May not be unique ○ Can change ○ Uses 32 or 128 bits ○ Can be static or dynamic
Static IP
● IP address that does not change each time a device connects to a network
Dynamic IP
● IP address that changes each time a device connects to a network
IPv
● Older version ● 4 groups of numbers (12 numbers total) ● Separated by full stops (.) ● Values 0-255 in each group ● 4 bytes long (32 bits) ● Represented in denary ● Fewer combinations possible
IPv
● Newer version ● 8 groups of numbers (32 numbers total) ● Separated by colons (:) ● Values 0-FFFF in each group ● 16 bytes long (128 bits) ● Consecutive groups of 0000 can be replaced with :: ● Represented in hexadecimal ● More combinations possible
Router
Managing Files
● Creates, moves, copies, pastes, deletes, names, renames, sorts files
Managing Peripherals and Drivers
● Installs drivers and manages data flow between computer and peripherals ● Drivers translate data between computer and peripherals
Managing Memory
● Controls data movement in hardware like RAM ● Ensures processes have enough memory ● Prevents two processes from accessing the same memory location ● Enables multitasking
Managing Multitasking
● Allows multiple simultaneous tasks using interrupts
Managing Interrupts
● Decides which interrupts to handle and when ● Uses interrupt queues based on priority
Other Functions
● Provides platform for running applications ● Manages user accounts
Interrupts
Types of Interrupts
Software Interrupts
● Division by zero ● Data from memory ● Output required ● Two processes accessing same data ● Request for input ● Null value
Hardware Interrupts
● Key press/click ● Mouse movement
● Mouse button click ● Hardware errors (e.g., printer out of paper) ● Hardware failure ● New hardware connected ● Paper jam in printer ● Printer out of paper
Interrupt Handling Process
● When FDE finishes or before next FDE, processor checks interrupt queue ● Checks if interrupt has higher priority than current task ● If so, stores current process in stack and fetches the interrupt ● Identifies interrupt source ● Calls relevant Interrupt Service Routine (ISR) ● When finished, returns to previous process or handles next high-priority interrupt ● If not, executes another FDE cycle
Programming Languages
High-Level Languages
● Closer to English, less like machine language ● Machine-independent (portable) ● Easy to debug ● One statement can represent many low-level statements
Low-Level Languages
● Uses mnemonics ● Closer to machine language (binary or assembly) ● Not portable (only runs on specific machine) ● Allows direct hardware manipulation ● Occupies less memory ● Used in embedded systems ● Provides full control ● Does not need conversion
Types of Low-Level Languages
● Machine Code: Binary code that computers directly understand ● Assembly Language: Uses mnemonics; requires assembler to translate to machine code
Translators
Compiler
5. The Internet and Its Uses
Internet vs. World Wide Web
● Internet is infrastructure; WWW is collection of websites ● Website is collection of web pages ● URL is text-based address of a web page (contains protocol, domain name, web page)
Web Communication
HTTP/HTTPS
● HTTP: Protocol for transmitting web pages and related data ● HTTPS: Secure version of HTTP ○ Combines HTTP with SSL/TLS ○ Encrypts data for transmission ○ Uses digital certificates for authentication
DNS (Domain Name Server)
● Contains website names and corresponding IP addresses
Process of Retrieving Web Pages
- User enters URL in browser
- Browser sends URL to DNS to find IP address
- If not found in one DNS, request forwarded to others
- Once IP address is found, browser requests web page using HTTP
- Web server sends data (HTML, CSS, scripts)
- Browser renders and displays web page
HTTPS Connection Process
- Web browser sends request to web server for digital certificate
- Web server sends certificate to browser
- Browser checks certificate authenticity
- If authentic, secure connection created
- Data sent is encrypted
- If not authentic, connection rejected
- Uses protocol such as SSL/TLS
Web Browsers
● SOFTWARE that allows users to view web pages and renders HTML ● Other functions: storing bookmarks, history, cookies, multitasking
Cookies
● TEXT FILES that store user preferences ● Stored by browser, sent between web server and browser ● Uses: ○ Track browsing habits ○ Store personal details ○ Tailor web pages to user's preferences ○ Store shopping cart items ○ Customize advertisements
Types of Cookies
● Session cookies: Stored in memory/RAM, deleted when browser closes ● Persistent cookies: Stored on hard drive, remain until deleted or expired
Digital Currency
● Exists only electronically and is decentralized ● Cryptocurrency: Digital currency that is encrypted ● Blockchain: Digital ledger with time-stamped records that cannot be altered
Computer Security Threats
Brute Force Attack
● Trial and error to guess a password ● Combinations repeatedly entered until correct password found ● Can be manual or automated ● Common combinations tried first ● Aims: ○ Steal/view/access data ○ Delete data ○ Change data ○ Lock accounts/encrypt data ○ Damage business reputation ● Solutions: ○ Strong passwords ○ Limited login attempts ○ Biometric authentication ○ Two-factor authentication
Data Interception
● Data packets intercepted and examined (using packet sniffers)
Malware Types
Virus
● Downloads to hard drive ● Replicates itself ● Corrupts data or uses resources ● Slows or crashes system
Worm
● Replicates itself ● Exploits vulnerabilities ● Clogs bandwidth ● Slows network
Spyware
● Records user actions ● Example: Keylogger ● Sends data to hackers ● Used to steal personal information
Trojan Horse
● Disguised as legitimate software ● Contains hidden malware ● Releases malware when downloaded
Adware
● Creates pop-ups and banner ads ● Often unwanted and intrusive
Ransomware
● Locks and encrypts data ● Demands payment for decryption
Effects of Malware
● Data may be deleted/changed ● Website may be deleted/changed ● Server may crash when filled with data
Malware Solutions
● Anti-virus software ● Anti-malware programs ● Firewall protection ● Cautious downloading ● Regular data backups
Online Threats
Pharming
● Malicious software redirects to fake websites ● Purpose: Obtain PERSONAL details ● User believes they're on legitimate site ● Solutions: ○ Anti-malware ○ Visual verification ○ Download only from trusted sources
Phishing
● Genuine-looking "bait" emails ● Contains disguised links to fake sites ● Prevention: ○ Verify email legitimacy ○ Check URL ○ Verify HTTPS ○ Avoid opening random emails
Social Engineering
● Psychological manipulation to obtain confidential data ● Purposes: ○ Data theft ○ Criminal activity ○ Hacking ○ Identity theft ○ Fraud ● Prevention: ○ Access levels ○ Awareness training
Access Levels
● Limited access to specific data ● Different permission levels for different users
