Computer System — NCERT Solutions

Given: We need to identify the software that makes a computer functional and state its two primary services.

Answer:

The software required to make a computer functional is the Operating System (OS).

Examples: Windows, Linux, macOS, Ubuntu.

Two Primary Services of an Operating System:

1. Process Management: The operating system manages the execution of processes (programs in execution). It schedules processes, allocates CPU time, and ensures that multiple processes can run efficiently without conflict.

2. Memory Management: The operating system manages the primary (main) memory of the computer. It keeps track of each memory location — whether it is free or occupied — and allocates/deallocates memory to processes as needed, ensuring maximum utilisation of available memory.

Given: A program is written in a high-level language (e.g., Python, C++, Java).

Concept: A computer can only understand machine code (binary language — 0s and 1s). It cannot directly understand high-level language instructions.

Answer:

A program written in a high-level language (called source code) must be translated into machine code (binary code) before the computer can execute it. This translation is done by special system software called translators, which are of the following types:

1. Compiler: Translates the entire source code into machine code at once, producing an executable file. The compiled machine code can then be executed directly by the CPU.

2. Interpreter: Translates and executes the source code line by line, one statement at a time.

3. Assembler: Converts assembly language code into machine code.

Thus, the computer understands a high-level language program only after it has been converted into machine code by a compiler or interpreter.

Given: Comparison between execution time of machine code and source code.

Concept: Execution time refers to the time taken by the CPU to run a program.

Answer:

The execution time of machine code is less than that of source code because:

• Machine code is already in binary form (0s and 1s), which is the language directly understood by the CPU. The CPU can execute machine code instructions directly without any translation, so no extra time is spent on conversion.

• Source code (written in a high-level language) must first be translated into machine code by a compiler or interpreter before the CPU can execute it. This translation process takes additional time.

Therefore, since machine code requires no translation step, its execution time is significantly less compared to source code, which requires translation before execution.

Given: We need to explain the need for RAM and differentiate it from ROM.

Need for RAM (Random Access Memory):

RAM is the primary working memory of a computer. It is needed because:

• It temporarily stores the data, instructions, and programs that are currently being used or processed by the CPU.
• The CPU can access data stored in RAM very quickly, making processing fast and efficient.
• Without RAM, the CPU would have to fetch data directly from slow secondary storage (like HDD), making the system extremely slow.
• It allows multiple programs to run simultaneously by holding their data in memory.

Difference between RAM and ROM:

Given: We need to explain why secondary memory is required in a computer system.

Answer:

Secondary memory (also called secondary storage or auxiliary memory) is needed for the following reasons:

1. Permanent Storage: RAM is volatile — it loses all data when the computer is switched off. Secondary memory provides permanent (non-volatile) storage for data, programs, and files even when the power is off.

2. Large Storage Capacity: RAM has limited storage capacity and is expensive. Secondary memory (e.g., Hard Disk Drive, SSD, USB drives) provides very large storage capacity at a much lower cost.

3. Storage of Programs and Files: All application software, operating system files, user documents, images, videos, and other data are stored permanently in secondary memory.

4. Backup and Portability: Secondary storage devices like pen drives and external hard disks allow users to back up data and carry it from one place to another.

Examples of secondary memory: Hard Disk Drive (HDD), Solid State Drive (SSD), CD/DVD, USB Flash Drive, Memory Card.

Given: We need to explain the communication mechanism between different components of a computer.

Answer:

Different components of a computer system communicate with each other through a set of electrical pathways called the System Bus.

The System Bus is a collection of wires/conductors that carry data, addresses, and control signals between the CPU, memory, and I/O devices. It consists of three types of buses:

1. Data Bus:

• Carries the actual data being transferred between components.
• It is bidirectional — data can flow both from CPU to memory/devices and from memory/devices to CPU.
• The width of the data bus (e.g., 8-bit, 16-bit, 32-bit, 64-bit) determines how much data can be transferred at one time.

2. Address Bus:

• Carries the memory address of the location where data is to be read from or written to.
• It is unidirectional — addresses flow only from the CPU to memory or I/O devices.
• The width of the address bus determines the maximum amount of memory that can be addressed.

3. Control Bus:

• Carries control signals from the CPU to coordinate and manage the activities of all components.
• Signals include read/write commands, interrupt signals, clock signals, etc.

Through these three buses working together, all components of the computer system communicate efficiently.

Given: We need to draw the block diagram of a computer system and describe each component.

Block Diagram of a Computer System:

$$\boxed{\text{Input Devices} \rightarrow \text{CPU (ALU + CU + Registers)} \leftrightarrow \text{Primary Memory (RAM/ROM)} \rightarrow \text{Output Devices}}$$

(Secondary Storage is connected to the CPU/Memory as well)

The block diagram consists of the following components connected via the System Bus:

Input Devices → CPU ↔ Primary Memory → Output Devices, with Secondary Storage also connected.

Functionality of Each Component:

1. Input Devices:

• Used to enter data and instructions into the computer.
• Examples: Keyboard, Mouse, Scanner, Microphone.
• They convert human-readable data into a form the computer can process.

2. CPU (Central Processing Unit):

• The brain of the computer. It has three sub-components:
• ALU (Arithmetic Logic Unit): Performs all arithmetic operations (addition, subtraction, etc.) and logical operations (comparisons).
• CU (Control Unit): Directs and coordinates all operations of the computer. It fetches instructions from memory, decodes them, and controls execution.
• Registers: Small, fast storage locations inside the CPU used to hold data and instructions currently being processed.

3. Primary Memory (RAM and ROM):

• RAM: Temporarily stores data and programs currently in use by the CPU. It is volatile.
• ROM: Stores permanent instructions like the BIOS. It is non-volatile.

4. Secondary Storage:

• Provides permanent, large-capacity storage for data and programs.
• Examples: HDD, SSD, CD/DVD, USB drives.

5. Output Devices:

• Display or present the processed results to the user.
• Examples: Monitor, Printer, Speakers.

6. System Bus:

• Connects all components and facilitates communication through the Data Bus, Address Bus, and Control Bus.

Given: We need to explain the role of the system bus and justify why the data bus is bidirectional while the address bus is unidirectional.

Primary Role of System Bus:

The System Bus is a set of electrical conductors (wires) that connects the CPU, primary memory, and I/O devices. Its primary role is to transfer data, memory addresses, and control signals between the various components of the computer system, enabling them to communicate and work together.

It consists of three parts: Data Bus, Address Bus, and Control Bus.

Why is the Data Bus Bidirectional?

The data bus carries actual data between the CPU and memory/I/O devices. Data needs to travel in both directions:

• From memory to CPU — when the CPU reads/fetches data or instructions from memory.
• From CPU to memory — when the CPU writes/stores processed results back to memory.

Since data must flow in both directions, the data bus is bidirectional.

Why is the Address Bus Unidirectional?

The address bus carries memory addresses that specify the location in memory where data is to be read from or written to. Addresses are always generated by the CPU and sent to the memory or I/O devices — the memory never sends an address back to the CPU.

Since the flow of addresses is always one-way (from CPU to memory/devices), the address bus is unidirectional.

Given: We need to differentiate between proprietary software and freeware software and give two examples of each.

Difference between Proprietary Software and Freeware Software:

Two Examples of Proprietary Software:

1. Microsoft Windows
2. Adobe Photoshop

Two Examples of Freeware Software:

1. VLC Media Player
2. Adobe Acrobat Reader (PDF Reader)

Given: We need to differentiate between microcontroller and microprocessor, and explain why smart home appliances use microcontrollers.

Difference between Microcontroller and Microprocessor:

Why do smart home appliances use a microcontroller instead of a microprocessor?

Smart home appliances (e.g., washing machines, microwave ovens, air conditioners, smart lights) use microcontrollers because:

1. Dedicated Task: These appliances are designed to perform specific, fixed tasks (e.g., controlling temperature, managing wash cycles). A microcontroller is ideal for such dedicated applications.

2. All-in-One: A microcontroller has the CPU, RAM, ROM, and I/O ports on a single chip, making it compact and easy to embed inside small appliances.

3. Low Cost: Microcontrollers are much cheaper than microprocessors, reducing the manufacturing cost of appliances.

4. Low Power Consumption: Microcontrollers consume very little power, which is important for battery-operated or energy-efficient devices.

5. Simplicity: The tasks performed by home appliances do not require the high processing power of a microprocessor, so a microcontroller is sufficient.

Given: We need to identify the different types of data encountered while browsing the Internet.

Answer:

While browsing the Internet, we deal with the following types of data:

1. Text Data: Web pages contain written content such as articles, news, descriptions, and messages (e.g., text on a website, emails, chat messages).

2. Image Data: Photographs, graphics, icons, and illustrations displayed on web pages (e.g., JPEG, PNG, GIF files).

3. Audio Data: Music, podcasts, voice messages, and audio clips streamed or downloaded from the Internet (e.g., MP3 files, online radio).

4. Video Data: Movies, video clips, tutorials, and live streams (e.g., YouTube videos, MP4 files).

5. Structured Data: Data organised in a fixed format such as tables, spreadsheets, or databases (e.g., stock market data, sports scores, product listings).

6. Semi-Structured Data: Data that does not follow a strict structure but has some organisational properties, such as HTML pages, XML files, and JSON data.

7. Unstructured Data: Data with no predefined format, such as social media posts, blog articles, comments, and forum discussions.

8. Hyperlinks: References/links that connect one web page to another.

9. Metadata: Data about data, such as file size, date of creation, author information embedded in files.