A blockchain is a shared database that thousands of computers hold copies of at once, where new records get added in batches called blocks and old records cannot be quietly changed. Nobody runs it, and no single party can edit it alone.
Bitcoin's blockchain has been running continuously since 3 January 2009, and every transaction ever made on it remains publicly readable today. That combination of permanence and openness is what the technology actually delivers, and it is narrower than most descriptions suggest.
The problem blockchains solve
Every traditional database has an owner. Your bank holds the record of your balance, and if that record says zero, it says zero. You are trusting the bank to keep it accurately and not to change it.
Where a trusted party exists, that works. It breaks down when parties who do not trust each other need to agree on a shared set of facts, because whoever holds the database can rewrite it.
Removing the owner is how blockchains solve it. Every participant holds the same copy, updates follow rules nobody can override alone, and altering history requires more resources than the attack could realistically return.
How the chain part works
Each block contains three things: a batch of transactions, a timestamp, and a cryptographic fingerprint of the block before it.
Tamper-evidence comes from that last part. A fingerprint, called a hash, is a fixed-length output generated from data, and changing even one character of the input produces a completely different output.
Say someone alters a transaction in block 500. That block's hash changes. Block 501 contains the old hash, so it no longer matches, and the mismatch cascades through every subsequent block. Rewriting one record therefore means rewriting every block after it, faster than the rest of the network is producing new ones.
How the network agrees
Distributed copies raise an obvious question: what happens when they disagree?
Consensus mechanisms answer it. Two dominate.
| Proof of Work | Proof of Stake | |
|---|---|---|
| Who adds blocks | Miners competing to solve a computational puzzle | Validators chosen partly at random, weighted by stake |
| Cost of participating | Hardware and electricity | Capital locked as stake |
| Cost of attacking | Out-computing the entire network | Acquiring and then risking a large share of stake |
| Used by | Bitcoin, Litecoin, Dogecoin | Ethereum, Solana, Avalanche, Cardano |
Both make attacks expensive rather than impossible. Proof of Work spends real resources on the puzzle. Proof of Stake puts capital at risk, since validators behaving dishonestly lose their stake.
Public, private, and permissioned
Not every blockchain is open, and the differences matter more than the shared label suggests.
- Public. Anyone can read, transact, and run a node. Bitcoin and Ethereum are the examples. Security comes from open participation.
- Private. One organisation controls who participates. Faster and cheaper, and a private blockchain with a single controlling party is closer to a database with extra steps.
- Permissioned or consortium. A defined group of organisations shares control. Used in supply chain and interbank settlement, where participants need a shared record without a single owner.
One useful test: if a single party can change the rules unilaterally, the decentralization is decorative.
What blockchains are actually good at
- Settlement without an intermediary. Value moves between parties directly, in minutes, at any hour.
- Auditable history. Every record is timestamped and public, so provenance can be traced years later.
- Programmable rules. Smart contracts execute automatically when conditions are met, without anyone administering them.
- Censorship resistance. No central operator exists to freeze an account or block a payment.
- Verifiable scarcity. Anyone can independently confirm exactly how many units exist, which is not possible with most assets.
What blockchains are bad at
Worth stating plainly, because the technology was sold as a general-purpose solution and never was one.
- Speed and cost at scale. Every node processing every transaction is inherently less efficient than a centralized server. Ethereum handles a fraction of what a payment network processes.
- Storing large data. On-chain storage is expensive, which is why NFTs usually hold a link rather than the file itself.
- Privacy. Public chains expose every transaction permanently. Pseudonymous is not anonymous.
- Fixing mistakes. Irreversibility protects against censorship and offers no recourse when you send funds to the wrong address.
- The input problem. A blockchain guarantees a record has not been altered, and guarantees nothing about whether it was true when written. Recording a false fact permanently just makes it a permanent false fact.
That last limitation is the one most "blockchain for X" proposals never resolved.
Where mb.io fits
Understanding the ledger is one thing. Getting access through a regulated crypto exchange to the assets running on it is another.
mb.io is a regulated crypto spot exchange backed by MultiBank Group, a financial institution founded in 2005 that serves more than 2 million clients across 100+ countries.
- Regulated by VARA in the UAE and AUSTRAC in Australia
- 10/10 security score from Hacken, an independent blockchain security auditor
- Institutional-grade MPC custody powered by Fireblocks, with segregated client funds
- A curated list of assets, so you're not sorting through thousands of tokens to find the ones worth trading
- Buy, sell, and swap in three steps, from sign-up to purchase
- 24/7 customer support, on web and on the iOS and Android apps
Open your account and start trading on mb.io.
Frequently asked questions
What is a blockchain in simple terms?
A shared record that many computers hold copies of at once. New entries are grouped into blocks, each block references the one before it cryptographically, and changing an old entry would require redoing every block after it.
Who controls a blockchain?
On a public blockchain, nobody individually. Rules are enforced by every node running the software, and changes require broad agreement. Private and permissioned chains do have controlling parties, which is the main practical difference.
Is blockchain the same as Bitcoin?
No. Bitcoin was the first application of blockchain technology, launched in January 2009. Thousands of networks now use the underlying structure for entirely different purposes.
Can a blockchain be hacked?
The core ledger of a large public chain has never been successfully rewritten, because the cost is prohibitive. Almost every major crypto theft has targeted something built on top: exchanges, bridges, wallets, or smart contracts.
Why are blockchain transactions irreversible?
Because reversal would require an authority with the power to override the ledger, and that authority is precisely what the design removes. Irreversibility is the trade-off for censorship resistance.
What is a block?
A batch of transactions bundled together with a timestamp and the cryptographic hash of the previous block. Bitcoin produces one roughly every ten minutes.
Do all blockchains use mining?
No. Mining is specific to Proof of Work. Proof of Stake networks, which include Ethereum since September 2022, use validators who lock up capital rather than miners spending electricity.
