January 2026 (Supplementary) Examination

The primary methods of I/O communication are:

1. Programmed I/O: The CPU constantly polls the I/O device's status register to check if it's ready. Very inefficient as it wastes CPU cycles.
2. Interrupt-driven I/O: The CPU issues a command to the I/O module and then does other work. When the I/O module is ready, it sends an interrupt signal to the CPU.
3. Direct Memory Access (DMA): The CPU grants an I/O module (DMA controller) authority to read from or write to memory directly, without CPU involvement. Used for large data transfers (e.g., disk reads), making the system much more efficient.

Characteristics:

• Uses non-volatile NAND flash memory instead of spinning magnetic platters.
• No moving parts, making them highly resistant to physical shock and completely silent.
• Much faster read/write speeds and drastically lower access latency than HDDs.

Block Diagram Concept:

[Host Interface (SATA/NVMe)] <--> [SSD Controller & Cache] <--> [NAND Flash Memory Chips]

Major components on a motherboard:

1. CPU Socket: Secures the processor and connects it directly to the motherboard pathways.
2. Memory Slots (DIMM): Holds the system's RAM sticks.
3. Chipset: Silicon chips that control traffic and data flow between the CPU, RAM, storage, and peripherals.
4. Expansion Slots (PCIe): Used to add dedicated graphics cards (GPUs), network cards, or other expansion cards.
5. Storage Connectors (SATA, M.2): Connect storage drives like HDDs and SSDs to the motherboard.
6. Power Connectors: Connects to the Power Supply Unit (PSU) to distribute power (e.g., 24-pin ATX).

Device Management is the OS component responsible for managing all hardware devices connected to the computer. Key Responsibilities:

1. Tracking Status: Keeps track of which devices are busy, free, or malfunctioning.
2. Allocation & Deallocation: Decides which process gets a device, when, and for how long. It allocates the device, and when the process is done, it deallocates it.
3. Device Drivers: Uses device drivers to facilitate seamless communication between generic OS commands and the specific hardware.

1. Binary (Base 2): Uses digits 0 and 1. It is the native language of computers, corresponding to the ON/OFF states of transistors.
2. Decimal (Base 10): Uses digits 0-9. The standard human notation. Used for input and output, but must be converted to binary internally.
3. Octal (Base 8): Uses digits 0-7. Used historically because it's easy to translate to binary (each octal digit is exactly 3 bits).
4. Hexadecimal (Base 16): Uses digits 0-9 and A-F. Extremely common in modern computing because one hex digit maps perfectly to 4 bits (a nibble), making large binary numbers easier to read.

• Assembly Language: A low-level programming language where there is a strong correspondence between the language's instructions and the architecture's machine code. It uses human-readable mnemonics (like ADD, MOV) instead of raw binary.
• Role of Assembler: An assembler is a translator program that takes assembly language code as input and converts (assembles) it into directly executable machine code (binary 1s and 0s).

Main Components:

1. Control Unit (CU): The brain of the CPU. Directs the fetch-decode-execute cycle and manages internal control signals.
2. Arithmetic Logic Unit (ALU): Performs mathematical calculations (addition, subtraction) and logical comparisons (AND, OR).
3. Registers: Ultra-fast, tiny storage locations inside the CPU holding data and instructions currently in use (e.g., PC, IR, ACC).

Block Diagram Concept:

[ Memory ] <--> [ Control Unit ] <--> [ Registers ]
                  \-- [ ALU ] --/

1. Data Transfer: Moves data between registers and memory. Example: MOV R1, R2 / LOAD R1, [Address]
2. Arithmetic: Performs math operations. Example: ADD R1, R2
3. Logical: Bitwise operations. Example: AND R1, R2
4. Control Flow / Branching: Changes execution path. Example: JMP [Address] (Jump to address) / CALL Function

Mesh Topology: Every device is connected to every other device (in a full mesh) or to several others (in a partial mesh).

• High Fault Tolerance: If one cable or node hardware fails, traffic is automatically routed around the failure using alternative pathways.
• High Uptime: Because there are redundant links, the network rarely experiences total outages.
• Applications: Military installations, core Internet backbone routers, and critical corporate infrastructure where downtime is unacceptable.

• Structure: An IPv4 address is a 32-bit numerical label assigned to a device. It is generally written in standard "dotted-decimal" notation, dividing the 32 bits into four 8-bit octets.
• Range: Each octet ranges from 0 to 255 (e.g., 192.168.1.1).
• Components: Each address consists of a Network ID (identifies the specific network) and a Host ID (identifies the specific device on that network). The subnet mask determines where the network ID ends and host ID begins.
• Example: 142.250.190.46 (a public Google IP).

• MAN (Metropolitan Area Network): Because the campuses are spread across a single city, a MAN (using fibre optics or leased lines from ISPs) can connect the various campus LANs into a single cohesive network.
• SD-WAN / VPN over Internet: For a more cost-effective secure connection, encrypted VPN tunnels over standard broadband can link the campuses.
• Client-Server Architecture: Centralised Active Directory servers, databases, and library servers hosted at the main campus are queried collectively by clients (students, faculty) across all campuses.
• Wireless Bridging: In cases with line-of-sight across parts of the city without easy cable routing, microwave or laser wireless point-to-point bridging may be utilized.

Client-Server Network: A centralized network architecture where powerful computers (servers) provide specific resources, security, or services, and terminal computers/devices (clients) request these services. Communication is strictly client-initiated. Real-world Example: Web Browsing: Your smartphone's Safari browser (the client) sends an HTTP request to an Amazon server (the server) for product page data. The server processes the request and sends back HTML, which your client browser renders for you.

HTML (HyperText Markup Language):

• Flexible, forgives missing closing tags or uppercase tags. Built on SGML.
• Advantages: Easy to learn, faster to code for beginners, browsers handle errors well.
• Disadvantages: Messy code can lead to cross-browser rendering differences.

XHTML (Extensible HyperText Markup Language):

• Stricter, fully standardized XML-based version of HTML.
• Advantages: Enforces clean, well-formed code (tags MUST be lowercase, properly nested, and closed). Easier for machines and automated scripts to parse consistently.
• Disadvantages: Steeper learning curve; a single syntax error can break page rendering entirely.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>My Simple Page</title>
</head>
<body>
  <h1>Welcome to the Page</h1>
  <p>This is a paragraph displayed below the heading.</p>
</body>
</html>

Explanation: We use JavaScript's setInterval method to execute a block of code every second. Inside this block, we calculate the difference between the target date and the current date (new Date()), convert that difference into days, hours, minutes, and seconds, and inject it into the HTML.

Sample Script:

let eventDate = new Date("Dec 1, 2026 09:00:00").getTime();
let timer = setInterval(function() {
  let now = new Date().getTime();
  let timeleft = eventDate - now;
  
  let days = Math.floor(timeleft / (1000 * 60 * 60 * 24));
  let hours = Math.floor((timeleft % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
  
  document.getElementById("countdown").innerHTML = days + "d " + hours + "h";
  
  if (timeleft < 0) {
    clearInterval(timer);
    document.getElementById("countdown").innerHTML = "Event Started";
  }
}, 1000);

1. Inline CSS (direct style attribute): <p style="color: blue;">Inline Text</p>

2. Internal CSS (within <style> block in <head>):

<style>
  p { color: red; }
</style>

3. External CSS (linking a separate .css file): <link rel="stylesheet" href="styles.css">