BSc CSIT (TU) Science Introduction to Information Technology (BSc CSIT, CSC109) Question Paper 2075 Nepal

Block Diagram of a Digital Computer

A digital computer is an electronic device that accepts data, processes it according to a set of instructions, and produces meaningful information as output. Its functional organisation is described by the following block diagram:

            +-------------------+
  INPUT --->|                   |---> OUTPUT
  UNIT      |   CPU             |     UNIT
            |  +------------+   |
            |  | Control    |   |
            |  | Unit (CU)  |   |
            |  +------------+   |
            |  | Arithmetic |   |
            |  | Logic Unit |   |
            |  | (ALU)      |   |
            |  +------------+   |
            +---------+---------+
                      |
              +-----------------+
              | MEMORY / STORAGE|
              +-----------------+

The solid arrows show the flow of data, while the Control Unit issues control signals to every other unit.

Functional Units

1. Input Unit Accepts data and instructions from the outside world, converts them into the binary form that the computer understands, and supplies them to the memory or CPU. Examples: keyboard, mouse, scanner.

2. Central Processing Unit (CPU) — the brain of the computer. It has two main parts:

• Arithmetic Logic Unit (ALU): Performs all arithmetic operations (addition, subtraction, multiplication, division) and logical operations (comparison, AND, OR, NOT). Intermediate results are held in registers.
• Control Unit (CU): Directs and coordinates all activities of the computer. It fetches instructions from memory, decodes them, and generates the timing/control signals that tell the other units what to do and when. It does not perform processing itself.
• Registers (within the CPU) are small, very fast storage locations that hold the data and instructions currently being processed.

3. Memory Unit (Storage Unit) Stores data, instructions, and intermediate/final results. It is of two types:

• Primary (main) memory — RAM and ROM; directly accessible by the CPU, fast but volatile (RAM).
• Secondary (auxiliary) memory — hard disk, SSD, etc.; large capacity, non-volatile, used for permanent storage.

4. Output Unit Converts the processed binary results into a human-readable form and presents them to the user. Examples: monitor, printer, speaker.

Summary

The input unit feeds data to memory, the CPU (ALU + CU) processes it, the memory holds data and results, and the output unit delivers the information — all under the supervision of the Control Unit.

Data Representation

Data representation is the method by which data (numbers, characters, symbols, images, etc.) is encoded into a form — ultimately a pattern of binary digits (0s and 1s) — so that it can be stored, processed, and transmitted by a digital computer. Since computers are built from two-state electronic components, all data is internally represented in binary. Character data is represented using standard coding schemes, the most important of which are ASCII, EBCDIC, and Unicode.

1. ASCII (American Standard Code for Information Interchange)

• A character-encoding standard developed in the USA, widely used in microcomputers and data communication.
• Standard ASCII uses 7 bits, so it can represent $2^7 = 128$ characters (codes 0–127): uppercase and lowercase English letters, digits 0–9, punctuation, and control characters.
• Extended ASCII uses 8 bits, representing $2^8 = 256$ characters, adding graphic and special symbols.
• Example: the letter A = $65$ = 1000001.

2. EBCDIC (Extended Binary Coded Decimal Interchange Code)

• An 8-bit coding scheme developed by IBM, used mainly on IBM mainframe and mid-range computers.
• With 8 bits it represents $2^8 = 256$ characters.
• It is not compatible with ASCII (the bit patterns for the same character differ), which is a drawback for data exchange between systems.

3. Unicode

• A universal character-encoding standard designed to represent the characters of all the world's languages (including Devanagari/Nepali, Chinese, Arabic, emojis, etc.) under a single scheme.
• It commonly uses 16 bits (UTF-16) giving $2^{16} = 65{,}536$ characters, and can be extended (UTF-8, UTF-32) to over a million code points.
• The first 128 Unicode code points are identical to ASCII, ensuring backward compatibility.

Comparison

The Internet

The Internet is a global, publicly accessible network of interconnected computer networks that communicate using a common set of protocols (the TCP/IP protocol suite). It links millions of private, public, academic, business, and government networks worldwide, allowing computers everywhere to exchange data and share resources. It is often called the network of networks.

Applications of the Internet

• Communication: email, instant messaging, video conferencing, VoIP.
• Information access and research: the World Wide Web, online libraries, search engines.
• E-commerce: online shopping, internet banking, digital payments.
• E-learning / online education: virtual classes, MOOCs, e-books.
• Entertainment: music and video streaming, online gaming, social media.
• E-governance: online tax filing, e-citizen services, public information portals.
• Telemedicine / e-health, job search, advertising, and remote work.

Services Provided by the Internet

1. World Wide Web (WWW): A collection of interlinked hypertext documents (web pages) accessed through web browsers using HTTP/HTTPS.

2. Electronic Mail (E-mail): Sending and receiving electronic messages and attachments using protocols such as SMTP, POP3, and IMAP.

3. File Transfer Protocol (FTP): Uploading and downloading files between a client and a remote server.

4. Telnet / Remote Login: Logging in to and operating a remote computer as if sitting in front of it.

5. Search Engines: Tools such as Google that index and locate information on the web.

6. Newsgroups / Discussion Forums / Social Networking: Online communities for sharing views and information.

7. Internet Telephony (VoIP) and Video Conferencing: Voice and video communication over the Internet (e.g., Skype, Zoom).

8. E-commerce and Internet Banking services.

Conclusion

The Internet has become an essential global infrastructure, providing diverse services and applications that transform communication, business, education, and daily life.

Classification of Computers Based on Size

Based on physical size, processing power, storage capacity, and cost, computers are classified into four main types:

1. Supercomputer

• The largest, fastest, and most powerful (and most expensive) computers.
• Capable of processing trillions of instructions per second; often use massive parallel processing.
• Used for weather forecasting, nuclear simulations, scientific research, and space exploration. Example: PARAM, Cray.

2. Mainframe Computer

• Large, powerful computers that support hundreds to thousands of users simultaneously via terminals.
• Used by big organisations such as banks, insurance companies, and government for bulk data processing. Example: IBM zSeries.

3. Minicomputer (Mid-range Computer)

• Medium-sized, less powerful and cheaper than mainframes; support a moderate number of users.
• Used in medium-sized businesses, departments, and as servers. Example: PDP-11.

4. Microcomputer

• The smallest and least expensive; built around a single microprocessor; designed mainly for a single user.
• Includes desktop PCs, laptops, tablets, and smartphones — the most widely used computers today.

Binary Addition: $10110 + 1101$

Align the numbers (the second number is padded with a leading 0) and add bit by bit from the right, carrying as in decimal but using base 2.

Binary addition rules: $0+0=0$, $0+1=1$, $1+1=10$ (write 0, carry 1), $1+1+1=11$ (write 1, carry 1).

   carries:  1 1 1 1
             1 0 1 1 0   (= 22)
           + 0 1 1 0 1   (= 13)
           -----------
             1 0 0 0 1 1  (= 35)

Step by step (right to left):

• $0+1 = 1$
• $1+0 = 1$
• $1+1 = 10$ → write $0$, carry $1$
• $0+1+1(\text{carry}) = 10$ → write $0$, carry $1$
• $1+0+1(\text{carry}) = 10$ → write $0$, carry $1$
• final carry $1$

Result: $10110_2 + 1101_2 = 100011_2$

Check: $22 + 13 = 35$, and $100011_2 = 32+2+1 = 35_{10}$. ✓

Compiler vs Interpreter

Both are language translators that convert a high-level source program into machine (object) code, but they differ in how they do it.

In short: a compiler translates the whole program before execution and is faster at run time, whereas an interpreter translates and runs one statement at a time and is easier for debugging.

Four Output Devices

An output device converts the processed binary results of the computer into a human-readable or usable form.

1. Monitor (Visual Display Unit): Displays text, images, and video on a screen. It gives soft copy output. Types include CRT, LCD, and LED monitors. Quality is measured by resolution (pixels) and refresh rate.

2. Printer: Produces hard copy (printed) output on paper. It may be an impact printer (e.g., dot-matrix, which strikes the paper) or a non-impact printer (e.g., inkjet, laser, which print without striking). Laser printers give high speed and quality.

3. Speaker: Produces audio (sound) output such as music, voice, and system sounds by converting digital signals into analog sound waves.

4. Plotter: A special output device that produces high-quality, large-size line drawings such as engineering drawings, maps, and architectural designs by moving a pen over the paper.

(Other valid examples: projector, headphones.)

Cache Memory

Cache memory is a small, extremely fast semiconductor (SRAM) memory placed between the CPU and the main memory (RAM). It stores copies of the data and instructions that the CPU is most frequently or most recently using, so the CPU can access them very quickly instead of fetching them from the comparatively slower main memory.

Cache is often organised in levels — L1 (smallest and fastest, inside the CPU), L2, and L3 (larger but slightly slower) — and works on the principle of locality of reference.

Importance of Cache Memory

• Speeds up processing: Bridges the speed gap between the very fast CPU and the slower RAM, reducing the CPU's idle waiting time.
• Improves system performance: Frequently used data/instructions are available immediately, increasing the hit ratio and overall throughput.
• Reduces main-memory traffic: Fewer accesses to RAM are needed, freeing the memory bus.
• Enhances CPU efficiency: Keeps the CPU busy with a steady supply of data, maximising utilisation.

In short, cache memory acts as a high-speed buffer that makes the computer run noticeably faster.

Types of Computer Networks (by geographical area)

1. LAN (Local Area Network)

• Connects computers and devices within a small geographical area such as a single room, building, or campus (typically up to about 1 km).
• High data-transfer speed, low cost, owned and managed by a single organisation.
• Uses media such as twisted-pair cable, coaxial cable, or Wi-Fi. Example: a network in a college computer lab or office.

2. MAN (Metropolitan Area Network)

• Spans a city or large metropolitan area (typically up to about 50 km), larger than a LAN but smaller than a WAN.
• Often connects several LANs within a city using high-speed links (e.g., fibre optics).
• Example: a cable-TV network or a network connecting all branches of a bank within a city.

3. WAN (Wide Area Network)

• Covers a very large geographical area — a country, continent, or the whole world.
• Connects many LANs and MANs using public/leased communication links such as telephone lines, satellites, and fibre. Lower speed and higher cost than LAN; usually not owned by a single organisation.
• Example: the Internet is the largest WAN.

Database and Advantages of a DBMS

Database: A database is an organised collection of logically related data stored in a systematic way so that it can be easily accessed, managed, and updated. For example, a college keeps a database of students containing their roll numbers, names, addresses, and marks.

A DBMS (Database Management System) is the software (e.g., MySQL, Oracle, MS Access) that creates, stores, manages, and provides controlled access to the database, acting as an interface between the user and the data.

Advantages of a DBMS

• Controlled data redundancy: Data is stored centrally, so unnecessary duplication of data is reduced or eliminated.
• Data consistency: With reduced redundancy, the same data does not appear in conflicting forms.
• Data sharing: Many users and applications can share the same data simultaneously.
• Data integrity: Validation rules and constraints keep the stored data accurate and reliable.
• Data security: Access can be restricted through user accounts, passwords, and permissions.
• Backup and recovery: Automatic facilities protect data against loss or failure.
• Data independence: Applications are insulated from changes in the physical storage of data.

Thus a DBMS provides efficient, secure, and consistent management of large volumes of data.

Transmission Media

Transmission media are the physical paths or channels through which data (signals) travel from one device to another in a network. They are broadly classified into guided (wired) and unguided (wireless) media.

A. Guided (Wired) Media

The signal travels along a solid physical conductor.

1. Twisted Pair Cable: Two insulated copper wires twisted together (UTP/STP). Cheap and easy to install; used in telephone lines and LANs. Limited speed and distance, prone to noise.

2. Coaxial Cable: A central copper conductor surrounded by insulation, a metallic shield, and an outer cover. Higher bandwidth and less noise than twisted pair; used in cable TV and older LANs.

3. Fibre-Optic Cable: Transmits data as pulses of light through thin strands of glass/plastic. Offers very high bandwidth and speed, long distance, and immunity to electromagnetic interference; but is costly and harder to install.

B. Unguided (Wireless) Media

Signals are transmitted through the air/space as electromagnetic waves, without a physical conductor.

1. Radio Waves: Omni-directional; used in radio, Wi-Fi, and mobile communication.

2. Microwaves: Line-of-sight, high-frequency waves used for long-distance terrestrial links between towers.

3. Infrared: Short-range communication (e.g., remote controls); cannot pass through walls.

4. Satellite Communication: Microwave signals relayed via satellites for very long-distance and global communication.

Short Note: Firewall

A firewall is a network-security system — implemented in hardware, software, or both — that monitors and controls the incoming and outgoing network traffic based on a predefined set of security rules. It sits between a trusted internal network (e.g., a private LAN) and an untrusted external network (e.g., the Internet), acting as a barrier that allows authorised traffic to pass while blocking unauthorised or malicious traffic.

Functions / Importance:

• Filters data packets and permits or denies them according to rules (based on IP address, port, protocol, etc.).
• Protects the internal network from hackers, unauthorised access, viruses, and other external threats.
• Hides internal network details from the outside world.
• Can log traffic for monitoring and auditing.

Types: packet-filtering firewall, stateful inspection firewall, proxy (application-gateway) firewall, and next-generation firewall.

In short, a firewall is the first line of defence that enforces an organisation's network-security policy.