Binary and Hexadecimal

Data Representation

• All data instructions in a computer are represented in binary
• Binary is the simplest numbering system
• It's represented by switches
• A bit is a binary unit, which can be either 0 or 1
• A byte is 8 bits
• Kilobytes, megabytes, gigabytes, and terabytes are all 1000 times larger than the previous unit
• Always show your working when converting between units
• The place value table is a simple method for converting between binary, hex and decimal
• The one's column is always on the right-hand side in the place value table
• Hexadecimal digits 0 to 9 are the same as decimal digits
• Letters are used to represent hexadecimal values between 10 and 15
• A in hexadecimal is 10 in decimal
• F in hexadecimal is 15 in decimal

Binary & Hexadecimal

• The purpose of hexadecimal is to shorten binary.
• One hexadecimal digit equals four binary digits.
• Perform binary addition like normal math, adding in columns.
• If the sum of a column is greater than 1, carry the remainder over to the next column
• A left shift in binary doubles a number by adding a 0 to the right side.
• A right shift in binary halves a number by removing the right digit and rounds down.

Character Sets

• Character sets provide a list with a binary representation for each character.
• ASCII is a character set that uses 7 bits for each character, allowing for 128 characters.
• Unicode is a character set with longer character codes, allowing representation of thousands of characters and multiple languages.
• For both ASCII and Unicode, character codes are sequential.

Bitmaps

• A bitmap image is made up of pixels (smallest dot of color)
• Image resolution is width x height
• Color depth is the number of bits per pixel, not the number of colors.
• File size = Image size x Color depth

Digital Sound

• Computers use digital sound in contrast to analog sound because analog sound is continuous and smooth.
• The sampling process takes measurements of the amplitude of a wave at regular intervals.
• Sampling rate is the number of sample measurements per second, measured in Hertz (Hz).
• Sample resolution is the color depth for sound which is the number of bits per sample.
• Increasing sampling rate, sample resolution, or sound duration increases quality, but also file size.
• File size (sound) = Sample rate x Sample resolution x Duration

Compression

• The goal of compression is to reduce file size.
• Compression is used for reducing storage space, shortening upload/download times.
• Lossy compression permanently removes data from the file, suitable for images and sound where quality loss is tolerable.
• Lossless compression rearranges file data to store it more efficiently, suitable for documents, programs where no data can be lost.

Huffman Coding

• Huffman coding is an example of lossless compression.
• Huffman coding gives frequently used characters the shortest character codes, unlike ASCII which uses equal length codes for every character.
• Each Huffman tree is unique to the specific text it was created for.
• To interpret a Huffman tree, start at the top, where numbers represent frequencies, and characters are at the bottom.
• Branches on the left represent 0, branches on the right represent 1.

Run-Length Encoding

• Run-length encoding stores data in frequency and value pairs.
• Pairs group consecutive characters or consecutive bits of data with their frequency.

Boolean Operators

• Boolean operators perform logic on 'true' or 'false' values, often represented as logic gates.
• NOT gate inverts an input.
• AND gate is true only if both inputs are true.
• OR gate is true unless both inputs are false.
• XOR gate (exclusive OR) is true only if one input is true and the other is false.

Software

• System software is designed for users and performs useful tasks, such as word processing or image editing.
• Application software supports running a computer and processes tasks needed for system functionality.
• Utility software is a type of application software focused on computer management, such as antivirus or compression.
• An Operating System (OS) manages hardware and programs on your computer, examples include Windows, Linux, and iOS.
• The OS manages the processor, scheduling instructions and switching rapidly between programs for multitasking.
• The OS also manages memory by loading programs and data into RAM.
• Input/output devices are plugged into the computer and require drivers to communicate with the system.

Programming Languages

• High-level languages, such as Java, Python, and C++, are more human-readable and portable than low-level languages.
• Low-level languages, such as assembly and machine code, are closer to what the CPU actually executes.
• Machine code is directly executed by the CPU and is composed of binary digits.
• Assembly is more readable than machine code, using decimal or bits of English.
• Assembly has a one-to-one correspondence with machine code (one assembly instruction = one machine code instruction).

Translators

• Translators convert high-level languages into machine code.
• Compilers translate the entire code at once and produce an executable file that can be executed independently.
• Interpreters translate and execute code one line at a time, which is helpful for debugging.

CPU

• The CPU (Central Processing Unit) executes program instructions using data.
• Components within the CPU include the ALU (Arithmetic Logic Unit) for math and logic calculations, the control unit that oversees all CPU operations, and the cache for storing frequently accessed data.
• The clock generates a consistent pulse to synchronize CPU components.
• Buses are collections of wires that connect CPU components.

Von Neumann Architecture

• The Von Neumann architecture uses a set of components, including the ALU, control unit, cache, and clock.
• CPUs follow the fetch-decode-execute cycle.

CPU Performance Factors

• Clock speed is the rate at which the fetch-decode-execute cycle occurs, usually measured in gigahertz (GHz).
• A higher clock speed means a faster CPU.
• Multi-core CPUs have multiple cores (processors) inside, allowing for parallel execution of instructions.
• Cache size affects performance; a larger cache holds more frequently used data, minimizing the need to access RAM.

Embedded Systems

• Embedded systems are computers integrated into other devices, with a specific purpose and limited functionality.
• Examples include household appliances, cars, and other devices.

Main Memory

• Main memory provides short-term storage for programs and data.
• RAM (Random Access Memory) is volatile, meaning data is lost when the power is turned off.
• ROM (Read Only Memory) is non-volatile, retaining data even when the power is off.
• ROM contains the program that starts the computer when it is turned on.

Secondary Storage

• Secondary storage is used for long-term storage of programs and data.
• It is non-volatile, meaning data persists even when the power is off.
• Examples of secondary storage include hard disk drives, optical drives, and solid-state drives.

Hard disk drives (HDDs)

• HDDs use magnetism to store data on a spinning disk, with a read/write head moving across the disk surface.
• HDDs are reliable, have large capacity, and are relatively inexpensive.
• HDDs are prone to damage due to their moving parts and can be noisy.

Solid-state drives (SSDs)

• SSDs store data electronically using logic gates and contain no moving parts.
• SSDs are faster than HDDs for reading and writing data and are more durable.
• SSDs are typically more expensive than HDDs for the same capacity.

Optical storage

• Optical drives use lasers to read and write data on a disc.
• Examples include DVDs and Blu-ray discs.
• Optical drives are portable, reliable, but less durable and have limited capacity per disc.

Cloud storage

• Data is stored in an offsite location and accessed via the internet.
• Examples include Dropbox, Google Drive, and Amazon Cloud storage.
• Cloud storage enables easy access to files from any location, scalability, and versatility.
• Cloud storage relies on the reliability and security of the cloud provider.

Networks

• A PAN (Personal Area Network) is a network used by a single person to connect devices like wireless headphones.
• A LAN (Local Area Network) covers a small geographical area, like a single building, and is typically owned and operated by a single organization.
• A WAN (Wide Area Network) spans a broader area, often including multiple buildings or locations, and is typically owned by multiple organizations.
• Both wired and wireless connections can be used in PAN, LAN, and WAN networks.

Network Topologies

• Network topology refers to the physical arrangement of devices in a network.
• Star topology connects each device to a central device, such as a router or access point.
• Bus topology uses a single cable to connect all devices.

Network Protocols

• Protocols are sets of rules that allow devices from different companies to communicate with each other.
• Protocols are layered, with each layer responsible for specific functions.

Layers of Network Protocol

• Application Layer: Handles interactions between applications, like web browsing, email, or file transfer.
• Transport Layer: Provides reliable data transfer between applications, including error handling and congestion control.
• Internet Layer: Handles addressing and routing packets between networks.
• Link Layer: Manages the physical transmission of data between devices on the same network segment, including error detection and correction.

Transmission Media

• Wired transmission media include copper cables, used extensively for LANs.
• Fiber optic cable transmits data using light pulses, offering high bandwidth and long-distance support.

Cyber Threats

• Pharming redirects website traffic to a counterfeit website, deceiving users.
• Data breaches expose confidential data by unauthorized users.
• Removable media includes devices like USB drives that can be easily removed from a computer, making them a risk for data theft or introducing malware.
• Unpatched software can contain vulnerabilities exploited by attackers.
• Weak passwords, including default passwords, are easily guessed or cracked by brute-force attacks.
• Social engineering tricks users into revealing information or giving up money.

Types of Social Engineering Attacks

• Baiting: Creating appealing scenarios, often with a reward, to deceive users into falling for a scam.
• Phishing: Using emails, text messages, or other communications to lure users into fake websites or information-gathering links.
• Shoulder surfing: Observing someone entering information, especially passwords.

Malware

• Malware is malicious software designed to harm computers or steal information.
• Viruses: Self-replicate, infecting other programs, spreading when the host program is run.
• Trojans: Hide within legitimate software, executing malicious actions once installed.
• Spyware: Collects personal information from a target computer without consent.

Cybersecurity Measures

• Penetration testing simulates real-world attacks to identify security weaknesses.
• White box penetration testing assumes the attackers have knowledge of the system.
• Black box penetration testing simulates an outsider's attack without prior knowledge of the system.
• Firewalls act as digital filters, checking incoming and outgoing network traffic and blocking packets that do not adhere to defined rules.
• MAC (Media Access Control) address filtering can be used to control access to a network based on the unique hardware address of a device.
• CAPTCHAs help identify human users by requiring them to solve visual puzzles or tasks that are difficult for bots to complete.
• Biometrics uses unique physical characteristics of a user, such as fingerprints, facial recognition, or voice recognition, for authentication.
• Antivirus software scans computers for known malware and attempts to remove it.
• Encryption scrambles data to make it unreadable without the correct key.

Databases

• A database organizes and stores data in a structured format.
• Tables contain organized data with rows (records) and columns (fields).
• Primary keys uniquely identify each record within a table.
• Foreign keys link tables together using a relationship (foreign key is a primary key from another table).
• Relational databases use foreign keys to link tables, reducing data redundancy and inconsistencies.

SQL Queries

• SQL (Structured Query Language) is used for interacting with databases.
• SQL queries are used to retrieve, insert, update, and delete data from databases.
• Select query extracts data from a database, using clauses: WHERE to filter data, ORDER BY to sort results, and FROM to specify the table.
• Insert query adds a new record into a table.
• Update query modifies existing records.
• Delete query removes records from a table.

Impacts of Computing

• Ethical issues: Examining the morality of technological development, including concerns like job displacement by automation, ethical implications of AI decisions, and social impacts.
• Environmental issues: Concerns about environmental impact, including resource consumption, disposal of electronic waste, and responsible sourcing of materials.
• Legal issues: Legal implications and regulations related to data protection, computer misuse, and intellectual property.
• Privacy issues: Concerns about the collection, use, and protection of personal data by governments, companies, and online services.