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Computer System – Class 11 Computer Science notes, important questions and MCQs

NCERT Class 11 Computer Science, chapter 1. Notes, key terms, important questions with answers and MCQs.

Chapter overview

A computer is an electronic device that takes data as input, processes it according to instructions, stores it and produces output. A computer system has hardware (physical parts) and software (programs). Its main components are input devices, the central processing unit (CPU), memory, storage and output devices, connected through buses. Computers evolved from mechanical calculators to modern microprocessor-based systems, and software ranges from system software to application software.

Components and memory

The CPU has the arithmetic logic unit (ALU) for calculations and comparisons, the control unit (CU) that directs operations, and registers for fast temporary storage.
Memory units: bit, nibble (4 bits), byte (8 bits), KB (1024 bytes), MB, GB, TB, PB; primary memory includes RAM (volatile, read-write) and ROM (non-volatile, read-only); cache memory is very fast memory between CPU and RAM.
Secondary storage (hard disk, SSD, pen drive, optical discs) is non-volatile and stores data permanently; data moves between components through the data bus, address bus and control bus.

Software and evolution

System software includes the operating system (which manages resources and provides a user interface), system utilities and device drivers; programming tools include language translators (assembler, compiler, interpreter).
Application software may be general-purpose (word processors, spreadsheets) or customised; software may be proprietary, freeware or free and open source (FOSS), such as Linux and Python.
Evolution: abacus, Pascaline, Babbage's Analytical Engine, ENIAC, transistors, integrated circuits, microprocessors (Intel 4004, 1971), personal computers and now mobile and cloud computing. Data may be structured, unstructured or semi-structured, and is processed through capture, storage, retrieval and deletion.

Key terms

Hardware: the physical components of a computer
CPU: the central processing unit that executes instructions
RAM: volatile primary memory used while programs run
Operating system: system software that manages hardware and provides a user interface
Compiler: a translator that converts a whole high-level program into machine code

Important questions with answers

Distinguish between RAM and ROM.2 marks

RAM (Random Access Memory) is volatile, read-write memory that holds data and programs currently in use. ROM (Read Only Memory) is non-volatile memory whose contents are written at manufacture and mainly read, such as the boot firmware.

What are the functions of an operating system?3 marks

An operating system manages processes, memory, files and input-output devices; it provides a user interface such as a command line or GUI; it manages security and access; and it acts as an interface between the user, application software and hardware.

Explain the components of a computer system with a block diagram description.5 marks

A computer system consists of input devices, the central processing unit, memory, storage and output devices, connected by buses. Input devices such as the keyboard, mouse, scanner and microphone convert data into a digital form the computer can process. The central processing unit (CPU) is the brain of the computer. It contains the arithmetic logic unit (ALU), which performs arithmetic operations such as addition and logical operations such as comparison; the control unit (CU), which fetches instructions from memory, decodes them and directs the other components; and registers, which are small, very fast storage locations inside the CPU. Primary memory holds data and instructions that the CPU is currently using. RAM is volatile and read-write, while ROM is non-volatile and holds startup instructions; cache memory, which is faster than RAM, stores frequently used data to speed up processing. Secondary storage devices, such as hard disk drives, solid state drives, pen drives and optical discs, store data permanently with large capacity. Output devices such as the monitor, printer and speakers convert processed digital data into a human-understandable form. Buses connect the components: the data bus carries data, the address bus carries memory addresses, and the control bus carries control signals. In a block diagram, input flows into the CPU, which communicates with memory and storage and sends results to output.

Quick revision

Input, CPU (ALU, CU, registers), output.
Memory units; RAM, ROM, cache; secondary storage.
Buses; system and application software.
Evolution of computers; data and its processing.

Exam tips

Remember: 1 byte = 8 bits; 1 KB = 1024 bytes.
Compare compiler (whole program at once) with interpreter (line by line).

Practice MCQs

1 byte is equal to
1. 4 bits
2. 8 bits
3. 16 bits
4. 1024 bits
Show answer
Answer: (b) 8 bits. A nibble is 4 bits.
Which memory loses its contents when power is switched off
1. RAM
2. ROM
3. hard disk
4. pen drive
Show answer
Answer: (a) RAM. RAM is volatile.
The part of the CPU that performs calculations is the
1. ALU
2. control unit
3. cache
4. bus
Show answer
Answer: (a) ALU. ALU stands for arithmetic logic unit.
A translator that converts and executes a program line by line is a/an
1. compiler
2. interpreter
3. assembler
4. linker
Show answer
Answer: (b) interpreter. Python commonly uses an interpreter.
Very fast memory placed between the CPU and RAM is
1. secondary memory
2. virtual disk
3. ROM
4. cache memory
Show answer
Answer: (d) cache memory. It stores frequently used data.
Linux is an example of
1. proprietary software
2. a device driver
3. hardware
4. free and open source software
Show answer
Answer: (d) free and open source software. Its source code is open.
The bus that carries the memory location to be read or written is the
1. address bus
2. data bus
3. control bus
4. USB
Show answer
Answer: (a) address bus. It is unidirectional from CPU.
Why is ROM used to store the boot program (firmware)
1. it is faster than cache
2. it can be easily erased by users
3. it is non-volatile, so instructions remain when power is off
4. it has unlimited capacity
Show answer
Answer: (c) it is non-volatile, so instructions remain when power is off. The computer needs startup instructions at power-on.

All chapters of Class 11 Computer Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.