Memory Hierarchy:

The memory hierarchy in a computer system is a structured arrangement of storage devices, organized based on speed, cost, and capacity. Its purpose is to provide an optimal balance between the high speed requirements of the CPU and the large storage capacity needed by applications, while keeping the overall system cost down. Data moves between these levels depending on its frequency of use, with the fastest and most expensive memory being closest to the CPU and holding frequently accessed data, and slower, cheaper, larger capacity memory further away holding less frequently accessed data.

Key characteristics of the hierarchy:

• Speed: Increases as one moves up the hierarchy towards the CPU (Registers > Cache > Main Memory > Secondary Storage).
• Cost per bit: Decreases as one moves down the hierarchy (Registers > Cache > Main Memory > Secondary Storage).
• Capacity: Increases as one moves down the hierarchy (Registers < Cache < Main Memory < Secondary Storage).

The typical levels of memory hierarchy include:

• Registers: Smallest, fastest, and most expensive memory, built directly into the CPU. They hold data currently being processed by the CPU.
• Cache Memory (L1, L2, L3): Very fast SRAM (Static RAM) that acts as a buffer between the CPU and main memory.
  • L1 Cache: Smallest and fastest cache, integrated directly into the CPU core.
  • L2 Cache: Larger and slightly slower than L1, often on the same chip but separate from the core.
  • L3 Cache: Largest and slowest cache, typically shared across multiple CPU cores.
• Main Memory (RAM - Random Access Memory): The primary working memory of the computer, typically DRAM (Dynamic RAM). It is much larger than cache but slower. Data must be loaded into RAM from secondary storage before the CPU can process it. It is volatile, meaning data is lost when power is off.
• Secondary Storage: Non-volatile storage devices used for long-term data retention, much larger and slower than main memory, and significantly cheaper per bit. Examples include Hard Disk Drives (HDDs), Solid State Drives (SSDs), and optical drives.

<<<GRAPHVIZ_START>>>
digraph MemoryHierarchy {
rankdir=TB;
node [shape=box, style=filled, fillcolor=lightblue];

Processor [label="CPU (Processor)"];
Registers [label="Registers"];
L1Cache [label="L1 Cache"];
L2Cache [label="L2 Cache"];
L3Cache [label="L3 Cache"];
MainMemory [label="Main Memory\n(RAM)"];
SecondaryStorage [label="Secondary Storage\n(HDD, SSD)"];

Processor -> Registers [label="Direct Access"];
Registers -> L1Cache [style=invis]; // Logical grouping
L1Cache -> L2Cache [dir=back, label="L1 (Fastest)"];
L2Cache -> L3Cache [dir=back, label="L2"];
L3Cache -> MainMemory [dir=back, label="L3"];
MainMemory -> SecondaryStorage [dir=back, label="RAM (Volatile)"];

{rank=same; Processor; Registers;}
{rank=same; L1Cache;}
{rank=same; L2Cache;}
{rank=same; L3Cache;}
{rank=same; MainMemory;}
{rank=same; SecondaryStorage;}

subgraph cluster_legend {
    label = "Hierarchy Characteristics";
    style = dashed;
    node [shape=plaintext, fillcolor=white];
    Legend1 [label="▲ Speed / Cost per bit"];
    Legend2 [label="▼ Capacity"];
}

// Invisible nodes to position legend
invisNode1 [style=invis, width=0, height=0];
invisNode2 [style=invis, width=0, height=0];
invisNode3 [style=invis, width=0, height=0];

Processor -> invisNode1 [style=invis];
invisNode1 -> invisNode2 [style=invis];
invisNode2 -> invisNode3 [style=invis];
invisNode3 -> Legend1 [style=invis];

Legend1 -> Legend2 [dir=none]; // Connect for vertical ordering

}
<<<GRAPHVIZ_END>>>

Types of Read-Only Memory (ROM):

Read-Only Memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be easily modified or can only be modified with difficulty or specific processes. It typically contains firmware, boot instructions, and other essential low-level programs that do not need to be changed frequently.

The main types of ROM include:

• Mask ROM (MROM):

  • Programmed during the manufacturing process by the semiconductor manufacturer.
  • Data is permanently "burned" into the chip by creating a specific mask pattern.
  • Cannot be changed or erased after manufacturing.
  • Lowest cost for large production volumes but has high initial setup costs due to mask creation.

• Programmable ROM (PROM):

  • Manufactured as a blank chip and can be programmed once by the user using a special device called a PROM programmer or "burner."
  • Contains an array of fuses (or anti-fuses) that can be selectively blown to store data.
  • Once programmed, it cannot be erased or reprogrammed.
  • More flexible than MROM for smaller production runs or custom applications.

• Erasable Programmable ROM (EPROM):

  • Can be programmed multiple times by the user.
  • Data is stored as an electrical charge on floating gates.
  • Erased by exposing the entire chip to strong ultraviolet (UV) light for a specific duration, which discharges the floating gates.
  • Identified by a transparent quartz window on top, which allows UV light to reach the silicon chip inside.
  • Reprogramming requires removal from the circuit, UV exposure, and then reprogramming using an EPROM programmer.

• Electrically Erasable Programmable ROM (EEPROM):

  • Can be programmed and erased electrically, without the need for UV light or removal from the circuit.
  • Data can be erased and reprogrammed byte by byte (or in small blocks).
  • Slower than RAM and has a limited number of erase/write cycles (typically tens of thousands to hundreds of thousands).
  • More convenient for in-system updates compared to EPROM.

• Flash Memory:

  • A type of EEPROM, but it is typically erased and programmed in large blocks or "pages" rather than byte-by-byte.
  • Offers faster erase and write speeds than traditional EEPROM for block operations.
  • High density and lower cost per bit compared to traditional EEPROM.
  • Widely used in modern devices like SSDs, USB flash drives, memory cards, and for storing firmware (BIOS/UEFI) in computers.

Comparison of System Software and Application Software

Types of System Software

• Operating System (OS):

  • The core software that manages all computer hardware and software resources.
  • Provides a user interface, manages memory, processes, files, and input/output operations.
  • Acts as an intermediary between the user/applications and the computer hardware.
  • Examples: Microsoft Windows, macOS, Linux, Android, iOS.

• Device Drivers:

  • Software that allows the operating system to communicate with specific hardware devices (e.g., printers, graphics cards, scanners).
  • Translates commands from the operating system into instructions that the hardware device can understand.
  • Each hardware component typically requires its own driver.

• Utility Software:

  • Designed to help analyze, configure, optimize, or maintain a computer system.
  • Performs tasks that improve the computer's performance, stability, or security.
  • Examples:
    • Antivirus software: Protects against malware.
    • Disk Defragmenters: Reorganizes data on a hard drive for faster access.
    • Backup software: Creates copies of data to prevent loss.
    • File compression tools: Reduces file sizes for storage or transmission.
    • Disk Cleaners: Removes unnecessary files to free up disk space.

• Firmware:

  • Low-level software embedded directly into hardware devices.
  • Provides basic control and instructions for the device's fundamental operations.
  • It is typically stored in non-volatile memory (like ROM or flash memory).
  • Examples: BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) in motherboards, firmware in routers, hard drives, and other embedded systems.

Benefits of Using Computer Networks

• Resource Sharing: Allows users to share hardware resources (e.g., printers, scanners), software applications, and data files across the network, reducing costs and improving efficiency.
• Enhanced Communication: Facilitates rapid and efficient communication among users through services like email, instant messaging, video conferencing, and shared calendars.
• Data Sharing and Centralization: Enables easy sharing and access to data from common servers, ensuring data consistency and simplifying data management and backup processes.
• Increased Reliability: Data can be replicated on multiple servers or storage devices within a network, providing redundancy and ensuring data availability even if one component fails.
• Cost-Effectiveness: Sharing resources and centralizing management reduces the need for individual hardware/software purchases and maintenance, leading to overall cost savings.
• Scalability: Networks can be expanded by adding more workstations, servers, or peripheral devices as the organization's needs grow, without significant overhaul.
• Centralized Management and Security: Network administrators can manage user accounts, apply security policies, and perform software updates from a central location, enhancing security and streamlining administration.

Types of Data Transmission Media

Data transmission media are the pathways that carry information from sender to receiver. They are broadly classified into two categories: Guided (Wired) Media and Unguided (Wireless) Media.

1. Guided Media (Wired)

Guided media use a physical link to transmit data signals. The signals are confined within a specific physical path.

• Twisted Pair Cable

  • Description: Consists of two insulated copper wires twisted together to reduce electromagnetic interference (EMI) from external sources and crosstalk between adjacent pairs.
  • Types:
    • Unshielded Twisted Pair (UTP): Most common type, widely used in Ethernet LANs and telephone systems. It is inexpensive, flexible, and easy to install. Categorized by performance levels (e.g., Cat5e, Cat6, Cat7).
    • Shielded Twisted Pair (STP): Similar to UTP but includes an outer metallic foil or braid shielding to provide better protection against noise and interference. It is more expensive and harder to install than UTP.
  • Characteristics: Moderate bandwidth, susceptible to noise (UTP), widely available, cost-effective for short to medium distances.
  • Applications: Local Area Networks (Ethernet), telephone lines.

• Coaxial Cable

  • Description: Features a central copper conductor surrounded by an insulating layer, which is then encased by a braided metallic shield and an outer insulating jacket. The concentric layers help to prevent signal loss and external interference.
  • Types: Thinnet (RG-58) and Thicknet (RG-11).
  • Characteristics: Higher bandwidth and better noise immunity than UTP, supports longer distances than twisted pair before signal attenuation becomes significant, but is more expensive than UTP.
  • Applications: Cable television distribution, older Ethernet networks (10BASE2, 10BASE5), and long-distance telephone transmission.

• Fiber Optic Cable

  • Description: Transmits data in the form of light pulses through thin strands of glass or plastic (optical fibers). Each fiber consists of a core (where light travels), cladding (reflects light back into the core), and an outer protective jacket.
  • Types:
    • Single-mode Fiber (SMF): Has a very small core diameter, allowing only a single path for light to travel. This results in minimal signal dispersion, enabling very high bandwidth and extremely long transmission distances.
    • Multi-mode Fiber (MMF): Has a larger core diameter, allowing multiple light paths. This leads to higher signal dispersion, limiting its use to shorter distances but making it cheaper and easier to terminate.
  • Characteristics: Extremely high bandwidth, very low signal attenuation, immune to electromagnetic interference (EMI), highly secure, but expensive to install and terminate.
  • Applications: High-speed internet backbones, long-haul telecommunications, data centers, and specialized industrial networks.

2. Unguided Media (Wireless)

Unguided media transmit data signals through the air or space, without a physical conductor. Signals are broadcasted and can travel in all directions or be focused.

• Radio Waves

  • Description: Electromagnetic waves generated by antennas, propagating through the air or vacuum. They can travel long distances and penetrate walls.
  • Characteristics: Omnidirectional propagation (can travel in many directions), relatively low frequency, susceptible to interference from other radio sources.
  • Applications: AM/FM radio broadcasting, cordless phones, Wi-Fi (at certain frequencies), cellular communication.

• Microwaves

  • Description: High-frequency electromagnetic waves that travel in straight lines (line-of-sight propagation).
  • Types:
    • Terrestrial Microwaves: Transmitted between ground-based antennas that must be in line of sight. Relayed over long distances using repeater stations.
    • Satellite Microwaves: Signals transmitted from an earth station to a satellite in orbit, which then retransmits them to another earth station.
  • Characteristics: Directional transmission (requires line of sight), high bandwidth, susceptible to atmospheric conditions (e.g., rain fade), widely used for long-distance communication.
  • Applications: Long-distance telephone and television transmission, cellular networks, satellite internet, radar systems.

• Infrared Waves

  • Description: High-frequency light waves (part of the electromagnetic spectrum) that are just below visible light. They travel in a straight line and cannot penetrate opaque objects.
  • Characteristics: Very high frequency, line-of-sight communication, limited range, highly secure within a room (cannot pass through walls), not affected by radio interference.
  • Applications: TV remote controls, wireless keyboards and mice, IrDA (Infrared Data Association) ports for short-range device communication, some short-range wireless LANs.

A digital computer is an electronic device that processes data represented in discrete values, typically binary (0s and 1s). It operates by performing arithmetic and logical operations on these discrete data units based on a stored program of instructions. Digital computers are general-purpose, programmable, and capable of high precision and flexibility.

Comparison of Digital Computers with Analog Computers:

Components of a CPU:

• Arithmetic Logic Unit (ALU): Performs all arithmetic operations (e.g., addition, subtraction) and logical operations (e.g., AND, OR, NOT, comparisons). It is the digital circuit responsible for computing.
• Control Unit (CU): Manages and coordinates all operations of the CPU and the computer. It fetches instructions from memory, decodes them, and then directs the other components of the CPU to perform the specified operations.
• Registers: Small, high-speed storage locations within the CPU that hold data and instructions temporarily during processing. Examples include the Program Counter (PC), Instruction Register (IR), Accumulator, and General-Purpose Registers.
• Cache Memory: A small, very fast memory integrated into the CPU chip or located very close to it. It stores copies of data from frequently used main memory locations to reduce access time and improve performance.

• Hard Copy Device: An output device that produces information in a tangible, physical form, typically printed on paper or other physical media, which can be permanently retained. Examples include printers and plotters.

• Soft Copy Device: An output device that displays information on a screen or in a temporary, volatile form, which is not permanently stored unless specifically saved. Examples include monitors, projectors, and speakers.

Six Human Data Entry Devices:

1. Keyboard
2. Mouse
3. Touchscreen
4. Microphone (for voice input)
5. Scanner
6. Graphics Tablet

ASCII Definition:

• ASCII stands for American Standard Code for Information Interchange.
• It is a character encoding standard that assigns unique numerical values (typically 7-bit binary codes) to characters.
• It encodes uppercase and lowercase English letters, digits (0-9), punctuation marks, and control characters.
• Purpose: To provide a consistent method for computers and other devices to represent and exchange text data.
• The original standard is 7-bit, allowing for 128 distinct characters. Extended ASCII uses 8 bits for 256 characters.

Base 10 to Base 2 Conversion (0.2345):
To convert a decimal fraction to binary, repeatedly multiply the fractional part by 2. The integer part of the product becomes the next binary digit, read from top to bottom.

1. 0.2345 × 2 = 0.4690
2. 0.4690 × 2 = 0.9380
3. 0.9380 × 2 = 1.8760
4. 0.8760 × 2 = 1.7520
5. 0.7520 × 2 = 1.5040
6. 0.5040 × 2 = 1.0080
7. 0.0080 × 2 = 0.0160

Therefore, 0.2345 (base 10) ≈ 0.0011110 (base 2)

Wearable computing refers to miniature electronic devices worn on the user's body as accessories, embedded in clothing, or implanted, designed to provide continuous, context-aware, and often hands-free interaction with computing resources.

Key characteristics:

• Always-on/Continuous Operation: Devices are typically active and accessible without explicit power-on.
• Context-awareness: Utilise sensors (e.g., GPS, accelerometers, heart rate) to understand the user's environment and physical state, providing relevant information proactively.
• Hands-free Operation: Often designed for minimal user input, relying on voice commands, gestures, or automatic data collection.
• Portability & Miniaturisation: Compact and lightweight, integrated seamlessly into daily life.
• Personalisation: Tailored to individual user needs and preferences, often providing biometric feedback or personalised alerts.

Examples:

• Smartwatches: Track fitness, display notifications, enable calls, and provide navigation.
• Fitness Trackers: Monitor activity levels, sleep patterns, and heart rate.
• Smart Glasses (Augmented Reality): Overlay digital information onto the real world view.
• Smart Clothing: Garments with integrated sensors for health monitoring or performance tracking.

Definition of Database:
A database is an organized collection of structured information, or data, typically stored electronically in a computer system. It is designed to facilitate the efficient storage, retrieval, modification, and management of data.

Benefits of Using Databases:

• Reduced Data Redundancy: Databases minimize the duplication of data, thereby saving storage space and preventing inconsistencies that arise from multiple copies of the same information.
• Improved Data Consistency: By reducing redundancy, databases ensure that data is consistent across the system. Changes made to data are reflected uniformly, preventing conflicting information.
• Enhanced Data Sharing: Databases allow multiple users and applications to access and share the same data concurrently, fostering collaboration and informed decision-making across an organization.
• Increased Data Security: Databases offer robust security features, including user authentication, access control mechanisms, and encryption, to protect sensitive data from unauthorized access, modification, or deletion.
• Better Data Integrity: Databases enforce integrity constraints (e.g., data types, validation rules, primary and foreign keys) to ensure the accuracy, validity, and reliability of the stored data.

Different characteristics of multimedia include:

• Digital: All multimedia components (text, images, audio, video) are converted into digital format, allowing for storage, processing, and transmission by computers.
• Integrated: Different media elements are combined and presented together in a synchronized and unified manner to create a coherent user experience.
• Interactive: Users have control over the presentation, sequence, and content of the multimedia application, allowing for active participation rather than passive consumption.
• Non-linear/Navigable: Users can navigate through the content in a non-sequential order, choosing their own path and accessing information based on their interests or needs.
• Dynamic/Time-dependent: Some media components, such as audio, video, and animation, evolve over time, requiring continuous playback and synchronization for proper presentation.

1. Definition of Cryptography:
Cryptography is the practice and study of techniques for secure communication in the presence of adversarial third parties. Its primary objectives are to ensure:

• Confidentiality: Preventing unauthorized access to information.
• Integrity: Ensuring information has not been altered by unauthorized entities.
• Authentication: Verifying the identity of users or systems.
• Non-repudiation: Preventing an entity from denying previous actions or commitments.

It involves converting information from a readable format (plaintext) into an unreadable format (ciphertext) using algorithms and keys, and vice versa.

2. Reasons for Firewall Usage:
Firewalls are network security devices or software that monitor and control incoming and outgoing network traffic based on predetermined security rules. They are used to:

• Prevent Unauthorized Access: Establish a barrier between a trusted internal network and untrusted external networks (e.g., the internet) to block malicious or unauthorized traffic.
• Control Network Traffic: Filter traffic based on source/destination IP addresses, port numbers, protocols, and application layer data, enforcing security policies.
• Protect Against Malware and Intrusions: Prevent the spread of viruses, worms, and other malware, and mitigate various forms of cyberattacks like denial-of-service (DoS) attacks or port scans.
• Enforce Security Policies: Allow network administrators to define specific rules for what traffic is permitted or denied, ensuring compliance with organizational security requirements.
• Monitor and Log Traffic: Record network activity, providing valuable data for security auditing, forensic analysis, and identifying potential threats.

Instruction Cycle

• The Instruction Cycle (also known as the Fetch-Decode-Execute Cycle) is the fundamental operation cycle of a computer's CPU. It describes the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction requires, and then carries out those actions.
• The cycle consists of three main stages:
  • Fetch: The CPU retrieves the next instruction from the main memory, at the address indicated by the Program Counter (PC), and loads it into the Instruction Register (IR). The PC is then incremented.
  • Decode: The Control Unit interprets the instruction in the IR to determine the operation to be performed and the operands involved.
  • Execute: The Control Unit directs the Arithmetic Logic Unit (ALU) or other components to perform the specified operation using the decoded operands. This may involve data transfer, arithmetic operations, or logical operations.
• Once the execution is complete, the cycle repeats for the next instruction.

BigData

• BigData refers to extremely large datasets that may be analyzed computationally to reveal patterns, trends, and associations, especially relating to human behavior and interactions. These datasets are too voluminous and complex to be dealt with by traditional data-processing application software.
• It is often characterized by the "3 Vs":
  • Volume: The sheer quantity of data generated and stored. It can be terabytes, petabytes, exabytes, or even larger.
  • Velocity: The speed at which data is generated, collected, and processed. This often involves real-time or near real-time processing.
  • Variety: The diverse types and sources of data, including structured data (databases), semi-structured data (XML, JSON), and unstructured data (text, images, audio, video, sensor data).
• BigData requires specialized tools and techniques for storage, processing, and analysis, often utilizing distributed computing frameworks.