Blockchain Technology Explained: How It Works and Why It Matters

Blockchain is a distributed ledger that records data in linked, cryptographically-sealed blocks, with no single authority controlling the chain.

That single-line definition does most of the work. Most confusion about blockchain comes from conflating it with Bitcoin (one application of the technology) or treating it as inherently complex when the core concept is straightforward. This article breaks down how the technology actually works, where it is being used in India, and what freshers in IT roles are expected to know about it.

What Blockchain Is (and Isn’t)

A blockchain is a database with two unusual properties. Its records are distributed across many computers simultaneously, and cryptographically linked so that altering any past entry requires rewriting every block that follows.

Each unit of storage is a “block,” and each block contains:

• The transaction data (a money transfer, a contract, a record update — whatever the application tracks)
• A hash of the current block’s contents (a fixed-length string computed from the data, unique to that exact set of bytes)
• The hash of the previous block (this is the “chain” — each block points back to the one before it)

The first block in any chain is the Genesis Block. It has no previous block to point to, so its “previous hash” field is conventionally set to all zeroes.

Changing any historical block changes that block’s hash. That broken hash no longer matches the “previous hash” reference in the next block. Fix that next block, and you break the one after it. You would need to rewrite every subsequent block, then convince the majority of the network to accept your rewritten version over the original. On a large public blockchain, that is computationally impractical (which is what “immutable” means in practice).

Blockchain is not Bitcoin. Bitcoin is one cryptocurrency that uses a blockchain as its transaction ledger. The blockchain technology itself is independent of Bitcoin and has been adapted for uses ranging from Ethereum smart contracts to enterprise supply chains.

How a Blockchain Transaction Actually Works

A transaction on a public blockchain goes through four steps:

• Step 1 — Initiation: The sender creates a new transaction (say, transferring an asset) and broadcasts it to the network.
• Step 2 — Verification: Every node in the network independently checks whether the transaction follows the rules (does the sender have sufficient balance? Is the cryptographic signature valid?). No single authority decides this; the network does.
• Step 3 — Block formation: Valid transactions are batched into a new block. For proof-of-work blockchains like Bitcoin, one node (the “miner”) solves a computationally expensive puzzle to earn the right to add the block. For proof-of-stake chains (like post-merge Ethereum), validators are chosen proportionally to their staked holdings — far less energy-intensive.
• Step 4 — Addition and propagation: The new block is added to the chain and broadcast to all nodes. Each node updates its copy of the ledger. The transaction is now permanent.

The IBM blockchain overview describes this consensus process in enterprise terms, where private blockchains often replace the energy-expensive mining step with a permission-based validation model.

Notice what is absent from those four steps: no bank, no clearing house, no government database. Intermediaries are replaced by cryptographic rules enforced by the network itself.

Where Blockchain Is Used in India Today

Blockchain moved beyond cryptocurrency discussions in India’s policy circles with NITI Aayog’s 2020 strategy document, which identified land records, pharmaceutical supply chains, educational credential verification, and financial services as priority domains.

Active pilots and deployments include:

• Land records: Andhra Pradesh and Telangana launched blockchain-based land registry pilots to reduce fraudulent property title transfers. The immutability property is the direct value here.
• Pharmaceutical supply chain: Tracking drug authenticity from manufacturer to pharmacy. A tamper-evident ledger prevents counterfeit drugs from entering the supply chain without detection.
• Educational credentials: Institutes including IIT Bombay have issued blockchain-verified degree certificates, letting employers verify credentials without calling the university.
• Payments infrastructure: NPCI (National Payments Corporation of India) has explored blockchain for cross-border remittances, where reducing intermediary fees matters.
• Enterprise applications: TCS, Infosys, and Wipro all run blockchain services practices, deploying Hyperledger Fabric for clients in banking, insurance, and logistics.

The pattern is consistent: blockchain earns its overhead cost in use cases where multiple distrusting parties need to share a tamper-evident record. Where a single trusted authority already controls the data, a conventional database is cheaper and faster.

The Real Trade-offs: What Blockchain Cannot Do Well

Every technology has failure modes. Blockchain’s are specific enough to summarise as a comparison:

Trade-off	Blockchain	Centralised alternative
Transaction throughput	Bitcoin: ~7/sec; Ethereum PoS: ~15/sec	Visa: 24,000+/sec; UPI handles 15B+ transactions/month
Energy cost	Proof-of-work is computationally expensive; PoS reduces this significantly	Negligible by comparison
Complexity	Distributed system; smart contract bugs are permanent	Single codebase, rollback possible
Reversibility	Hard fork required for correction (contentious on public chains)	Database rollback or admin override

Source: throughput figures from IBM’s blockchain overview and public network statistics.

High-profile exploits of DeFi protocols in 2021 and 2022 resulted in losses of hundreds of millions of dollars, all from smart contract code errors rather than cryptographic failures. The immutability that makes blockchain trustworthy also makes bugs permanent.

These are engineering trade-offs, not reasons to dismiss the technology. They explain why blockchain is valuable in specific niches (multi-party trust, public auditability) and a poor fit for others (high-throughput payments, systems requiring frequent corrections).

What Freshers Need to Know for Technical Rounds

Blockchain is not a core topic in most campus placement tests. It does appear in technical discussions at IT services companies, and dedicated roles tagged “blockchain developer” or “distributed systems” require it specifically.

What the must-know technical questions framework applies here: interviewers care whether you understand the concept and can reason about trade-offs, not whether you’ve memorised terminology.

Concepts worth being able to explain in a technical round:

• Distributed vs. decentralised: Distributed means data is stored across multiple nodes. Decentralised means no single entity controls the system. Blockchain is both. A cloud database replicated across data centres is distributed but not decentralised.
• Hash functions: A cryptographic hash function maps input data to a fixed-length string. The same input always produces the same output; a tiny change in input produces a completely different output. SHA-256 is what Bitcoin uses.
• Consensus mechanisms: Proof-of-work vs. proof-of-stake. Know the trade-off (security vs. energy cost) rather than implementation details.
• Smart contracts: Self-executing code on a blockchain, introduced by Ethereum. Worth understanding even if your role doesn’t involve writing them.
• Public vs. private blockchain: Public chains (Bitcoin, Ethereum) are open to anyone. Private or permissioned chains (Hyperledger Fabric) restrict participation — common in enterprise deployments.

For roles in consulting-track companies where you might advise clients on technology choices, the KPMG recruitment process guide shows how technical discussions in consulting interviews differ from coding-centric rounds. Trade-off reasoning matters more than implementation depth in those settings.

Companies like Cadence work at the hardware-software boundary where distributed systems concepts appear in different contexts. The Cadence interview preparation guide covers the kind of systems-level reasoning that overlaps with distributed ledger concepts.

Blockchain’s distributed transaction model is easier to internalise when you trace it through an actual implementation rather than describing it in the abstract. TinkerLLM lets you paste a smart contract snippet or a hash chain implementation and ask what each line does, why the consensus step requires the previous hash, and where the system breaks under adversarial input. That active reasoning about the technology sticks far better than re-reading the same description. At ₹299 on TinkerLLM, that is the cost of one campus interview prep book.