Computer Science – XI

(1) ASCII code is basically  (iii) 7 bit code

Reason: ASCII uses 7 bits → can represent 2⁷ = 128 characters.

(2) Pseudo code is used in  (ii) Program design

Reason: Pseudo code is written during the design phase to plan the logic before coding.

(3) FTP is  (i) File Transfer Protocol

(4) When multiple computers are capable of processing then it is  (ii) Distributed computing

Program design is the process of planning the solution to a problem before writing actual code. It involves breaking the problem into smaller logical steps and deciding how each step will be solved.

Tools used in program design:

• Algorithm – step-by-step logical instructions
• Flowchart – graphical representation of logic
• Pseudo code – English-like description of program logic

Importance: Good program design reduces errors, saves time, and makes coding easier.

i) (2CBA)₁₆ = ( ? )₂

Convert each hexadecimal digit to its 4-bit binary equivalent:

ii) (1101101.1101)₂ = ( ? )₁₆

Group bits in sets of 4 from the decimal point (left = integer, right = fraction):

An algorithm is a finite, well-defined, step-by-step set of instructions written to solve a particular problem.

Properties of an Algorithm:

1. Input – Takes zero or more inputs
2. Output – Produces at least one output
3. Definiteness – Each step is clear and unambiguous
4. Finiteness – Must end after a finite number of steps
5. Effectiveness – Each step must be simple and practically executable

i) (1F8)₁₆ = ( ? )₂

ii) (1F8)₁₆ = ( ? )₁₀

A transmission medium is the physical or wireless path through which data travels from sender to receiver in a network.

Types:

1. Wired (Guided):
   • Twisted Pair Cable – used in telephone and LAN
   • Coaxial Cable – used in cable TV
   • Optical Fiber – uses light; very high speed
2. Wireless (Unguided):
   • Radio Waves – used in FM, Wi-Fi
   • Microwave – used in long-distance communication
   • Satellite – covers large areas globally
   • Infrared – short-range (TV remote)

Centralized computing is a type of computing in which all processing is done by one central, powerful computer (usually a mainframe or server). Other terminals (called dumb terminals) are connected to this central computer.

The terminals only send requests and display results — they do no processing themselves.

Advantages:

• Easy to manage and maintain
• All data is stored in one place (centralized control)
• Better security

Disadvantages:

• If central computer fails, the entire system stops working
• Heavy load on the central computer

i) ASCII (American Standard Code for Information Interchange):

• ASCII is a 7-bit character encoding standard.
• It can represent 2⁷ = 128 characters including letters, digits, and symbols.
• Example: 'A' = 65 in decimal = 1000001 in binary.
• Used to store and transmit text in computers.

ii) BCD (Binary Coded Decimal):

• In BCD, each decimal digit is separately converted to its 4-bit binary equivalent.
• Example: 25 in BCD = 0010 0101
• Used in calculators and digital displays.

i) WWW (World Wide Web):

• The WWW is a system of interlinked hypertext documents accessed over the internet using a browser.
• It was invented by Tim Berners-Lee in 1989.
• Example: Visiting www.google.com – your browser loads a web page stored on a server.

ii) E-Commerce (Electronic Commerce):

• E-Commerce means buying and selling of goods and services over the internet.
• Types: B2B (Business to Business), B2C (Business to Consumer), C2C (Consumer to Consumer).
• Example: Amazon, Flipkart – users browse products, place orders, and pay online.

Networking: Networking means connecting two or more computers together using communication links so they can share data and resources (printers, internet, etc.).

Types of Networks:

• LAN – Local Area Network (within a building)
• MAN – Metropolitan Area Network (a city)
• WAN – Wide Area Network (countries/worldwide)

Protocol: A protocol is a set of rules that governs communication between computers in a network. It ensures data is sent and received correctly.

Examples of Protocols: TCP/IP, HTTP, FTP, SMTP, POP3.

i) (A9B)₁₆ = ( ? )₁₀

ii) (0011011101)₂ = ( ? )₁₀

iii) (3905)₁₀ = ( ? )₁₆

Verification: 15×256 + 4×16 + 1 = 3840 + 64 + 1 = 3905 ✓

E-Mail (Electronic Mail) is a method of sending and receiving messages digitally over the internet. It allows users to send text, files, and attachments instantly to any person with an email address.

Components of E-Mail:

• Sender's email address
• Receiver's email address
• Subject, Body, and Attachments

Protocols used:

• SMTP (Simple Mail Transfer Protocol) – for sending email
• POP3 / IMAP – for receiving email

Example: yash@gmail.com

1. Multiple users can work on the same project simultaneously from different locations.
2. Improves productivity and reduces the time to complete tasks.
3. Resources such as files, printers, and internet are shared easily.
4. Easy communication through email, video conferencing, and messaging tools.
5. Helps in decision making as different people can contribute ideas.
6. Cost-effective as resources are shared among users.

i) (98.58)₁₀ = ( ? )₂

ii) (2E.8)₁₆ = ( ? )₁₀

1. Input: An algorithm takes zero or more inputs from the user.
2. Output: It must produce at least one output or result.
3. Definiteness: Every step must be clear, precise, and unambiguous.
4. Finiteness: The algorithm must end after a finite number of steps.
5. Effectiveness: Each step must be basic, simple, and practically possible to execute.

Pseudo code is an informal, English-like description of a program's logic. It is not written in any specific programming language — it uses simple English statements to describe steps.

Features:

• Easy to understand by non-programmers
• Used in program design phase
• No special syntax rules — just simple logic

Example (Find if a number is positive or not):

The double-double method is used to convert a binary number to decimal. Start from the leftmost bit, double it, and add the next bit. Repeat until all bits are used.

Example: (1101)₂ = ( ? )₁₀

Verification: 1×8 + 1×4 + 0×2 + 1×1 = 8+4+0+1 = 13 ✓

A flowchart is a graphical or diagrammatic representation of the steps of an algorithm or program using standard symbols connected by arrows.

Standard Flowchart Symbols:

i) 1010 − 101

ii) 1001 − 1110

1. Makes the logic of a program easy to understand visually.
2. Helps in detecting errors (debugging) in the program logic.
3. Acts as a guide during coding — programmer follows the flowchart.
4. Useful for documentation — others can understand the program easily.
5. Helps in communication between team members working on the same project.
6. Simplifies complex logic into clear, understandable steps.

In a client-server network, computers are divided into two roles:

• Server: A powerful computer that stores data and provides services (files, internet, printers) to other computers.
• Client: A computer that requests services from the server.

Features:

• Centralized control and management
• Better security — data is stored on the server
• Easy to add more clients (scalable)
• If the server fails, clients cannot access resources

In distributed computing, processing is spread across multiple computers connected through a network. Each computer handles part of the task simultaneously, and the results are combined.

Advantages:

• Fault tolerant – if one computer fails, others continue working
• Faster processing due to parallel computation
• Easily scalable by adding more computers
• Efficient use of resources
• No single point of failure

i) A + B = ?

ii) A − B = ?  (using 2's complement method)