Draw a basic block diagram of a computer system and describe the functions of the various hardware blocks. Also, distinguish among Internet, Extranet and Intranet.

A computer system accepts data and instructions, processes them according to a program, stores data or results, and presents useful information. Its basic functional blocks are the input unit, central processing unit, memory/storage unit, and output unit.

Basic block diagram

                         ┌───────────────────────┐
                         │     Main Memory       │
                         │   RAM, ROM, Cache     │
                         └──────────↕────────────┘
                                    ↕
┌──────────────┐     ┌───────────────┴────────────────┐     ┌──────────────┐
│  Input Unit  │ ──→ │      Central Processing Unit   │ ──→ │ Output Unit  │
│Keyboard, etc.│     │  Control Unit + ALU + Registers│     │Monitor, etc. │
└──────────────┘     └───────────────↕────────────────┘     └──────────────┘
                                    ↕
                         ┌───────────┴───────────┐
                         │  Secondary Storage   │
                         │    SSD, HDD, USB      │
                         └───────────────────────┘

The blocks communicate through data, address and control paths. Although the diagram separates them by function, the processor repeatedly exchanges instructions and data with memory and input/output controllers.

Functions of the hardware blocks

1. Input unit: It receives data and instructions from users or the environment and converts them into machine-readable signals. A keyboard enters text, a mouse provides pointing commands, and a scanner converts a paper image into digital form. The input unit sends this prepared data to memory or the CPU.

2. Central Processing Unit (CPU): The CPU executes program instructions and coordinates the entire system.

   • The Control Unit (CU) fetches instructions from memory, decodes them, issues control signals and directs the sequence of operations.
   • The Arithmetic Logic Unit (ALU) performs arithmetic operations such as addition and subtraction, logical operations such as AND and OR, and comparisons such as greater than or equal to.
   • Registers are very small, fastest storage locations inside the CPU. They hold the current instruction, addresses, data and intermediate results. Examples include the program counter, instruction register and accumulator.

3. Main memory: It holds programs, input data and intermediate results that the CPU needs quickly. RAM is volatile working memory and loses its contents when power is removed. ROM is non-volatile and stores permanent startup instructions. Cache, located in or close to the CPU, keeps frequently used instructions and data to reduce access time.

4. Secondary storage: Devices such as SSDs, hard disks and USB drives provide long-term, non-volatile storage. They have much greater capacity than main memory but are generally slower. Programs and files are loaded from secondary storage into RAM before active processing.

5. Output unit: It converts processed results into a form people or other systems can use. A monitor displays visual output, a printer produces hard copy, and speakers produce sound.

Internet, Intranet and Extranet

All three may use TCP/IP, web browsers and web technologies, but they differ mainly in ownership and authorized access.

Basis	Internet	Intranet	Extranet
Meaning	The worldwide public network of interconnected networks	A private network used inside one organization	A controlled extension of an intranet for selected outsiders
Users	Anyone with network access	Authorized employees or internal members	Employees plus approved suppliers, customers or partners
Scope and ownership	Global; no single owner	Owned and managed by one organization	Managed by an organization and securely shared with external parties
Main purpose	Public information, communication and online services	Internal communication, documents and applications	Secure inter-organizational collaboration and data exchange
Security	Public exposure requires strong endpoint and service security	Protected by accounts, permissions and often an internal firewall	Requires authentication, authorization and commonly VPN or encrypted web access
Example	A public search engine or news website	A company HR and leave-management portal	A supplier portal used to check stock and submit orders

Thus, the Internet is public, an Intranet is private to an organization, and an Extranet gives limited, protected access to trusted external users.