NEB Class 11 · Past paper
The complete NEB Class 11 2076 exam paper for Computer Science, all 15 questions with solved model answers.
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What is Boolean algebra? Describe AND and NAND gates with logic symbol, truth table and Venn diagram. [4+6]
Boolean algebra is a branch of mathematics that deals with variables having only two possible values, $0$ (false/low) and $1$ (true/high), and with logical operations (AND, OR, NOT) performed on them. It is the mathematical foundation used to design and simplify digital logic circuits.
AND gate The AND gate gives output $1$ only when all inputs are $1$. Boolean expression: $Y = A \cdot B$. Logic symbol: a D-shaped body with a flat input side and two inputs $A$, $B$.
| A | B | Y = A.B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Venn diagram: two overlapping circles $A$ and $B$; only the intersection (overlap) region is shaded, representing $A \cdot B$.
NAND gate The NAND gate is an AND gate followed by a NOT gate; its output is $0$ only when all inputs are $1$, and $1$ otherwise. Boolean expression: $Y = \overline{A \cdot B}$. Logic symbol: an AND gate symbol with a small bubble (circle) at the output.
| A | B | Y = (A.B)' |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Venn diagram: two overlapping circles $A$ and $B$; everything except the intersection is shaded, representing $\overline{A \cdot B}$.
Draw the block diagram of computer system. Explain the input and processing units. [4+6]
Block diagram of a computer system:
+-------------+ +----------------------+ +-------------+
Input ->| Input Unit | ----> | Central Processing |----> | Output Unit | -> Output
+-------------+ | Unit (CPU) | +-------------+
| +----------------+ |
| | Control Unit | |
| | ALU | |
| | Registers | |
| +----------------+ |
+----------+-----------+
|
+------v------+
| Memory Unit |
+-------------+
Input unit: The input unit is used to feed data and instructions into the computer. Input devices such as the keyboard, mouse, scanner and microphone accept information from the user, convert it into a binary (machine readable) form and send it to the CPU or memory for processing. Thus the input unit forms the entry point of data into the system.
Processing unit (CPU): The CPU, called the brain of the computer, processes the data supplied by the input unit. It has three parts:
What is Operating System (OS)? Describe its functions in brief. [2+8]
An operating system (OS) is system software that acts as an interface between the user and the computer hardware. It manages all the resources of the computer and provides an environment for running application programs. Examples: Windows, Linux, macOS, Android.
Functions of an operating system:
1. Process management - creates, schedules and terminates processes and allocates CPU time among them so several programs can run.
2. Memory management - keeps track of main memory, allocates and frees memory for processes and handles virtual memory.
3. File management - organises data into files and folders and controls creating, reading, writing, saving and deleting files with access permissions.
4. Device management - controls input/output devices through device drivers and manages data transfer between them and the CPU.
5. Security and protection - protects data and resources using passwords and access rights and prevents unauthorised access.
6. User interface - provides a way to interact with the computer, either a command line interface (CLI) or a graphical user interface (GUI).
7. Error detection and handling - detects errors in hardware and software and takes corrective action.
What is programming language? Describe the various types of programming language with their merits and demerits. [2+8]
A programming language is a set of symbols, words and grammar rules used to write instructions that a computer can understand and execute to solve a problem.
Types of programming language with merits and demerits:
1. Machine level language - written in binary ($0$ and $1$).
2. Assembly language - uses mnemonic codes (ADD, MOV) and an assembler.
3. High level language - English like statements (C, C++, FORTRAN) needing a compiler/interpreter.
4. Fourth generation language (4GL) - non procedural, near natural language (SQL).
In general, higher level languages are easier for humans but run slower and give less direct control over hardware than low level languages.
Differentiate between analog and digital computer. [5]
Difference between analog and digital computer:
| Analog computer | Digital computer |
|---|---|
| Works on continuous data (physical quantities) | Works on discrete data (digits 0 and 1) |
| Measures quantities such as voltage, pressure, temperature | Counts data and performs arithmetic/logical operations |
| Output is usually in the form of graphs or signals | Output is in numbers, text or graphics |
| Lower accuracy | Very high accuracy |
| Difficult to program, special purpose | Easy to program, general purpose |
| Example: speedometer, thermometer, voltmeter | Example: desktop PC, laptop, calculator |
Convert (513)10 Decimal number to (..)2 Binary number. [5]
Convert $(513)_{10}$ to binary by repeated division by $2$ and reading the remainders from bottom to top.
$$ \begin{aligned} 513 \div 2 &= 256\ \text{r } 1 \ 256 \div 2 &= 128\ \text{r } 0 \ 128 \div 2 &= 64\ \text{r } 0 \ 64 \div 2 &= 32\ \text{r } 0 \ 32 \div 2 &= 16\ \text{r } 0 \ 16 \div 2 &= 8\ \text{r } 0 \ 8 \div 2 &= 4\ \text{r } 0 \ 4 \div 2 &= 2\ \text{r } 0 \ 2 \div 2 &= 1\ \text{r } 0 \ 1 \div 2 &= 0\ \text{r } 1 \end{aligned} $$
Reading the remainders from bottom to top: $$(513)_{10} = (1000000001)_2$$
Check:
$$ \begin{aligned} (1000000001)_2 &= 2^9 + 2^0 \ &= 512 + 1 \ &= 513 \end{aligned} $$
Verified.
What is ROM? List out the different types of ROM. [2+3]
ROM (Read Only Memory) is a non volatile primary memory whose contents can normally only be read and not written by the user during operation. It retains its data even when the power is switched off and usually stores permanent instructions such as the BIOS/bootstrap program needed to start the computer.
Different types of ROM:
Describe the DeMorgan's Law. [5]
DeMorgan's laws are two important theorems of Boolean algebra that relate the AND, OR and NOT operations. They are used to simplify Boolean expressions and to convert between AND/OR forms. First law: the complement of a sum equals the pr...
What is secondary memory? Explain about hard disk. [2+3]
Secondary memory (auxiliary storage) is non volatile memory used to store data, programs and information permanently. It is not directly accessed by the CPU, has a large capacity, is cheaper and slower than primary memory, and keeps its data even when the power is off. Examples: hard disk, CD/DVD, pen drive, SSD.
Hard disk: A hard disk (Hard Disk Drive, HDD) is the main secondary storage device of a computer. It consists of one or more rigid circular metal platters coated with a magnetic material, mounted on a spindle that rotates at high speed. Data is stored magnetically in concentric tracks and sectors, and read/write heads move across the surfaces to read or record data. Key points:
Differentiate between CLI and GUI operating system. [5]
Difference between CLI and GUI operating systems: CLI (Command Line Interface) GUI (Graphical User Interface) ------ User interacts by typing text commands User interacts using graphics: icons, menus, windows Commands must be memorised a...
Explain the compiler and interpreter. [5]
A compiler and an interpreter are both language translators that convert high level source code into machine (object) code, but they work differently. Compiler: it translates the entire source program into machine code at once and create...
Define social media. Describe negative impact of social media. [2.5+2.5]
Social media refers to websites and applications that let users create, share and exchange information, ideas, photos and videos and interact with one another through online communities and networks. Examples: Facebook, Instagram, X (Twitter), YouTube and TikTok.
Negative impacts of social media:
Explain the <OL> tag and <img> tag with its properties and values. [2.5+2.5]
<OL> tag (Ordered List):
The <ol> tag in HTML creates an ordered (numbered) list, in which each item is placed inside an <li> (list item) tag. It is a container (paired) tag.
1 (numbers, default), A/a (uppercase/lowercase letters), I/i (uppercase/lowercase Roman numerals).start="5".Example:
<ol type="A" start="2">
<li>Computer</li>
<li>Printer</li>
</ol>
<img> tag (Image):
The <img> tag inserts an image into a web page. It is an empty (unpaired) tag.
src="photo.jpg".Example:
<img src="photo.jpg" alt="My Photo" width="200" height="150">
What are the features of spreadsheet? Explain. [5]
A spreadsheet is application software that stores data in a grid of rows and columns and lets the user calculate, analyse and present numeric data. Example: MS-Excel. Its main features are:
A1), making it easy to arrange.SUM, AVERAGE, IF and COUNT perform automatic calculations, and results update when data changes (automatic recalculation).Write short notes on: a) URL b) Mobile computing. [2.5+2.5]
a. URL (Uniform Resource Locator)
A URL is the unique address of a resource (web page, image or file) on the Internet that tells the browser where the resource is located and how to fetch it. A typical URL has the form:
https://www.example.com/page.html
It consists of the protocol (https), the domain name (www.example.com) and the path/file name (/page.html). By typing a URL or clicking a link, the browser locates and displays the correct web page.
b. Mobile computing Mobile computing is the technology that lets users transmit data, voice and video and access information through portable wireless devices (smartphones, tablets, laptops) without being tied to a fixed physical connection. It relies on wireless networks such as Wi-Fi and mobile data (4G/5G). Its benefits include mobility, anytime anywhere access, real time communication and location based services, which is why it is widely used for banking, e-learning, navigation and social media.
Boolean algebra is a branch of mathematics that deals with variables having only two possible values, (false/low) and (true/high), and with logical operations (AND, OR, NOT) performed on them. It is the mathematical foundation used to design and simplify digital logic circuits.
AND gate The AND gate gives output only when all inputs are . Boolean expression: . Logic symbol: a D-shaped body with a flat input side and two inputs , .
| A | B | Y = A.B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Venn diagram: two overlapping circles and ; only the intersection (overlap) region is shaded, representing .
NAND gate The NAND gate is an AND gate followed by a NOT gate; its output is only when all inputs are , and otherwise. Boolean expression: . Logic symbol: an AND gate symbol with a small bubble (circle) at the output.
| A | B | Y = (A.B)' |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Venn diagram: two overlapping circles and ; everything except the intersection is shaded, representing .
A programming language is a set of symbols, words and grammar rules used to write instructions that a computer can understand and execute to solve a problem.
Types of programming language with merits and demerits:
1. Machine level language - written in binary ( and ).
2. Assembly language - uses mnemonic codes (ADD, MOV) and an assembler.
3. High level language - English like statements (C, C++, FORTRAN) needing a compiler/interpreter.
4. Fourth generation language (4GL) - non procedural, near natural language (SQL).
In general, higher level languages are easier for humans but run slower and give less direct control over hardware than low level languages.
Convert to binary by repeated division by and reading the remainders from bottom to top.
Reading the remainders from bottom to top:
Check:
Verified.