Class | Subject | Book | Chapter | Session | Questions covered |
|---|---|---|---|---|---|
XI | Computer Science | Computer Science (NCERT) | 1 – Computer System | 2026-27 | 22 of 22 |
Chapter at a glance
Idea | Key point |
|---|---|
Computer system | Hardware (CPU, memory, input and output devices) + software |
CPU | Control Unit (CU) + Arithmetic Logic Unit (ALU) + registers |
Memory | Primary: RAM (volatile), ROM (non-volatile); secondary: HDD, SSD, pen drive |
System bus | Data bus, address bus, control bus |
Software | System software (OS, drivers, utilities), programming tools (editor, compiler, interpreter, assembler), application software |
Data | Structured, semi-structured and unstructured |
Units | 1 KB = 1024 B; 1 MB = 1024 KB; 1 GB = 1024 MB |
Exercise Questions
Name the software required to make a computer functional. Write down its two primary services.
Answer
Answer
The software required to make a computer functional is the operating system (OS). Its two primary services are:
- Resource management: it controls and allocates the processor, memory, files and I/O devices to the programs that need them.
- Providing an interface (and running programs): it acts as an interface between the user and the hardware (through a GUI or command line) and helps to load and run application software.
Operating system; services: management of hardware resources, and an interface between the user and the computer.
How does the computer understand a program written in high level language?
Answer
Answer
A computer understands only machine language (binary 0s and 1s). A program written in a high-level language (source code) must therefore be translated by a language translator:
- A compiler translates the whole program into machine code (object code) at once and reports all the errors.
- An interpreter translates and executes the program line by line.
The CPU then executes the resulting machine code.
A compiler or an interpreter translates the high-level program into machine code, which the CPU executes.
Why is the execution time of the machine code less than that of source code?
Answer
Answer
Machine code is already in the binary form that the CPU can execute directly, so no translation is required at run time. Source code must first be translated by a compiler or interpreter; with an interpreter this is done every time the program runs, line by line, which takes extra time.
Machine code runs directly on the CPU, whereas source code needs translation during execution.
What is the need of RAM? How does it differ from ROM?
Answer
Answer
Need of RAM: the CPU needs fast storage for the programs and data that it is currently working on; RAM (Random Access Memory) provides this working space, and gives quick access to any location.
Basis | RAM | ROM |
|---|---|---|
Full form | Random Access Memory | Read Only Memory |
Nature | Volatile: contents are lost when power is off | Non-volatile: contents remain |
Use | Stores programs and data currently in use | Stores permanent instructions, such as the boot program (firmware) |
Read / write | Can be read and written | Normally only read |
Speed and size | Fast, larger capacity | Small capacity |
RAM is the volatile working memory for running programs; ROM is permanent memory holding start-up instructions.
What is the need for secondary memory?
Answer
Answer
Primary memory (RAM) is volatile, costly and limited in size. Secondary memory is needed to:
- Store data and programs permanently, even when the power is switched off.
- Provide large storage capacity at a lower cost per byte (hard disk, SSD, pen drive, DVD).
- Back up and carry data from one computer to another.
Data is moved to RAM only when it is needed by the CPU.
It stores large amounts of data and programs permanently and cheaply, which RAM cannot do.
How do different components of the computer communicate with each other?
Answer
Answer
The components communicate through the system bus, a set of wires or lines that connect the CPU, memory and I/O devices. It has three parts:
- Data bus: carries data.
- Address bus: carries the address of the memory location or device.
- Control bus: carries control signals (read, write, clock, interrupts).
Peripheral devices communicate through ports and device controllers connected to this bus.
Through the system bus (data, address and control buses).
Draw the block diagram of a computer system. Briefly write about the functionality of each component.
Answer
Answer
Component | Functionality |
|---|---|
Input unit | Takes data and instructions from the user and converts them into a form the computer can use (keyboard, mouse, scanner, microphone) |
Control unit (CU) | Directs the flow of data and instructions between the components, and decides which operation to do next |
Arithmetic logic unit (ALU) | Performs arithmetic (add, subtract…) and logical (compare, AND, OR) operations |
Memory unit | Stores data, instructions and results: primary (RAM, ROM) for current use, and secondary for permanent storage |
Output unit | Presents the processed results to the user (monitor, printer, speaker) |
The CU and ALU together form the CPU, the brain of the computer.
Input → CPU (CU + ALU) ↔ memory → output, as shown in the block diagram above.
What is the primary role of system bus? Why is data bus is bidirectional while address bus is unidirectional?
Answer
Answer
Primary role: the system bus transfers data, addresses and control signals between the CPU, memory and I/O devices.
- Data bus is bidirectional because data has to move both ways: from the CPU to memory/devices (write) and from memory/devices to the CPU (read).
- Address bus is unidirectional because only the CPU sends the address of the location it wants to access; memory and devices never send addresses back to the CPU.
The system bus carries data, addresses and control signals; data flow in both directions, but addresses flow only from the CPU.
Differentiate between proprietary software and freeware software. Name two software for each type.
Answer
Answer
Basis | Proprietary software | Freeware |
|---|---|---|
Cost | Has to be purchased from the vendor who holds the copyright | Available free of cost |
Source code | Not available to the user | Usually not available either, so it cannot be modified |
Rights | User gets only the right to use under a license; copying or sharing is restricted | Free to use and share, but cannot be changed or sold |
Examples | Microsoft Windows, Tally (also Quickheal) | Skype, Adobe Reader |
Proprietary software is paid and copyright-restricted (Windows, Tally); freeware is free to use but not modifiable (Skype, Adobe Reader).
Write the main difference between microcontroller and microprocessor. Why do smart home appliances have a microcontroller instead of microprocessor embedded in them?
Answer
Answer
Basis | Microprocessor | Microcontroller |
|---|---|---|
Chip contents | Only the CPU; RAM, ROM and I/O must be attached externally | CPU, RAM, ROM and I/O peripherals on one chip |
Use | General-purpose computers | Specific tasks in embedded devices |
Cost and power | Costly, higher power and larger | Cheap, low power and small |
Why in smart appliances: devices such as washing machines, microwave ovens and smart TVs do a fixed set of tasks. A microcontroller is compact, cheap, consumes little power and has everything needed on a single chip, so it is more suitable than a microprocessor.
A microcontroller has CPU, memory and peripherals on one chip; it is cheaper and smaller, so it suits dedicated appliances.
Mention the different types of data that you deal with while browsing the Internet.
Answer
Answer
While browsing, we deal with:
- Text: web pages, articles, e-mails, chat messages.
- Images: photos, graphics, icons.
- Audio: songs, podcasts, voice messages.
- Video: clips, films, live streams.
- Numerical and tabular data: prices, scores, forms and database records.
- Web data formats: HTML pages, links, cookies, files for download (PDF, spreadsheets).
By structure, these are structured (tables and database records), semi-structured (HTML, XML, e-mail) and unstructured (free text, images, audio and video) data.
Text, images, audio, video, numbers and web documents, i.e. structured, semi-structured and unstructured data.
Categorise the following data as structured, semi-structured and unstructured:
• Newspaper • Cricket Match Score • HTML Page • Patient records in a hospital
Answer
Answer
Data | Category | Reason |
|---|---|---|
Newspaper | Unstructured | Free text and pictures with no fixed format |
Cricket match score | Structured | Fixed fields (team, runs, wickets, overs) in tabular form |
HTML page | Semi-structured | No rigid format, but tags separate the elements |
Patient records in a hospital | Structured | Stored in database tables with fixed fields (name, age, diagnosis) |
Newspaper – unstructured; cricket score – structured; HTML page – semi-structured; patient records – structured.
Name the input or output device used to do the following:
a) To output audio b) To enter textual data c) To make hard copy of a text file d) To display the data or information e) To enter audio-based command f) To build 3D models g) To assist a visually-impaired individual in entering data
Answer
Answer
Task | Device |
|---|---|
a) Output audio | Speaker (or headphones) |
b) Enter textual data | Keyboard |
c) Hard copy of a text file | Printer |
d) Display data or information | Monitor (screen) |
e) Enter audio-based command | Microphone |
f) Build 3D models | 3D printer (output device) |
g) Help a visually-impaired person enter data | Braille keyboard (or speech input using a microphone) |
- Speaker b) Keyboard c) Printer d) Monitor e) Microphone f) 3D printer g) Braille keyboard
Identify the category (system, application, programming tool) of the following software:
a) Compiler b) Assembler c) Ubuntu d) Text editor
Answer
Answer
Software | Category | Reason |
|---|---|---|
a) Compiler | Programming tool | Translates a high-level program into machine code |
b) Assembler | Programming tool | Translates assembly language into machine code |
c) Ubuntu | System software | It is an operating system |
d) Text editor | Programming tool | Used to type and store the source code of a program |
- programming tool b) programming tool c) system software d) programming tool
Explore Yourself
Question E1
Ask your teacher to help you locate any two device drivers installed on your computer.
Answer
Steps (Windows): right-click Start → Device Manager → expand a category → right-click a device → Properties → Driver. On Linux (Ubuntu): Additional Drivers or the command lsmod.
Examples of device drivers: the display (graphics) driver and the audio (sound) driver (others: printer, network adapter, keyboard).
E.g. display driver and audio driver, found through Device Manager.
Question E2
Write any two system software and two application software installed on your computer.
Answer
- System software: an operating system such as Windows 11 or Ubuntu, and a device driver or a utility such as disk clean-up / antivirus.
- Application software: a word processor (MS Word / LibreOffice Writer) and a web browser (Chrome).
System: Windows/Ubuntu, device driver. Application: LibreOffice Writer, Chrome browser.
Question E3
Which microprocessor does your personal computer have? Which generation does it belong to?
Answer
Method: Windows – Settings → System → About, or Task Manager → Performance → CPU. Linux – the command lscpu.
Sample answer: “Intel Core i5-12400, 12th generation” (the first digits after the series, here 12, show the generation).
Personal activity; e.g. Intel Core i5 (12th generation), as shown in System → About.
Question E4
What is the clock speed of your microprocessor?
Answer
Clock speed is the number of cycles a CPU performs per second, measured in GHz. It is shown along with the processor name in Settings → About or in Task Manager. Sample: 2.5 GHz (2.5 billion cycles per second).
Personal activity; e.g. 2.5 GHz.
Question E5
Name any two devices in your school or home that have a microcontroller.
Answer
Washing machine and microwave oven (others: air conditioner, TV remote, digital camera, smart watch, traffic light controller).
Washing machine and microwave oven.
Question E6
Check the size of RAM and HDD of a computer in your school. Make a table and write their size in Bytes, Kilobytes, Megabytes and Gigabytes.
Answer
Sample: RAM = 8 GB and HDD = 500 GB, using 1 KB = 1024 B, 1 MB = 1024 KB, 1 GB = 1024 MB.
Memory | Gigabytes | Megabytes | Kilobytes | Bytes |
|---|---|---|---|---|
RAM | 8 | 8,192 | 8,388,608 | 8,589,934,592 |
HDD | 500 | 512,000 | 524,288,000 | 536,870,912,000 |
Table above (sample values; use the actual sizes of your school computer).
Question E7
List all secondary storage devices available at your school or home.
Answer
Hard disk drive (HDD), solid-state drive (SSD), pen drive (USB flash drive), memory card (SD card), CD/DVD and external hard disk (and magnetic tape in large installations).
HDD, SSD, pen drive, memory card, CD/DVD, external hard disk.
Question E8
Which operating system is installed on your computer at home or school?
Answer
Personal activity. Check by right-clicking This PC → Properties (Windows), or by running lsb_release -a in Ubuntu. Example: Windows 11 at home and Ubuntu 22.04 in the school computer lab.
E.g. Windows 11 / Ubuntu.
Topic checklist
- ☒ Operating system and software types (Q1, Q9, Q14, E2)
- ☒ Language translators (Q2, Q3)
- ☒ Memory: RAM, ROM, secondary (Q4, Q5, E6, E7)
- ☒ Components and buses (Q6, Q7, Q8)
- ☒ Microprocessor vs microcontroller (Q10, E3 – E5)
- ☒ Data types and devices (Q11 – Q13)