What Is a Block?
A block = One page in the blockchain ledger.
If the blockchain is the entire book, each block is simply a single page filled with transactions.
---
1. What's Inside a Block?
Think of a block like a shipping container. For Bitcoin, a new one is sealed every ~10 minutes. For $ETH , it's every ~12 seconds.
Inside each container, you'll find:
Component What It Means
Transaction data Who sent what to whom — e.g., "Ali → Sara: 0.1 $BTC "
Timestamp Exact time the block was created
Block number Like page #1,234,567
Previous block's hash A fingerprint of the page before it — this links them together
This block's hash The block's own unique fingerprint
Nonce / Miner info Proof that someone did the work to validate it
---
2. How Blocks Connect
```
Block #100 → Block #101 → Block #102 → Block #103
↑ ↑ ↑
contains hash contains hash contains hash
of #99 of #100 of #101
```
This is what makes it a chain.
Change one transaction in Block #100, and its hash changes. Then Block #101 no longer recognizes it, and every block after breaks. You'd have to redo the entire chain — practically impossible.
---
3. Block vs. Transaction
Transaction Block
What it is One transfer — e.g., Ali sends Sara 5 $USDT A batch of ~1,000–5,000 transactions grouped together
Speed Instant to submit Takes time to confirm
Analogy A single payment slip A whole batch file sent to the bank
Miners or validators collect pending transactions, bundle them into a block, and add it to the chain.
---
4. Different Blockchains = Different Speeds
Blockchain Block Time Transactions Per Block
Bitcoin ~10 minutes 2,000 – 3,000
Ethereum ~12 seconds 150 – 300
Solana ~0.4 seconds 2,000+
Faster blocks = faster payments. But often, that comes with trade-offs in security or decentralization.
---
5. Why Blocks Matter
Blocks are what make blockchain immutable.
Because each block locks onto the previous one, you can't rewrite history without redoing all the work that came after it.
A block = One page in the blockchain ledger.
If the blockchain is the entire book, each block is simply a single page filled with transactions.
---
1. What's Inside a Block?
Think of a block like a shipping container. For Bitcoin, a new one is sealed every ~10 minutes. For $ETH , it's every ~12 seconds.
Inside each container, you'll find:
Component What It Means
Transaction data Who sent what to whom — e.g., "Ali → Sara: 0.1 $BTC "
Timestamp Exact time the block was created
Block number Like page #1,234,567
Previous block's hash A fingerprint of the page before it — this links them together
This block's hash The block's own unique fingerprint
Nonce / Miner info Proof that someone did the work to validate it
---
2. How Blocks Connect
```
Block #100 → Block #101 → Block #102 → Block #103
↑ ↑ ↑
contains hash contains hash contains hash
of #99 of #100 of #101
```
This is what makes it a chain.
Change one transaction in Block #100, and its hash changes. Then Block #101 no longer recognizes it, and every block after breaks. You'd have to redo the entire chain — practically impossible.
---
3. Block vs. Transaction
Transaction Block
What it is One transfer — e.g., Ali sends Sara 5 $USDT A batch of ~1,000–5,000 transactions grouped together
Speed Instant to submit Takes time to confirm
Analogy A single payment slip A whole batch file sent to the bank
Miners or validators collect pending transactions, bundle them into a block, and add it to the chain.
---
4. Different Blockchains = Different Speeds
Blockchain Block Time Transactions Per Block
Bitcoin ~10 minutes 2,000 – 3,000
Ethereum ~12 seconds 150 – 300
Solana ~0.4 seconds 2,000+
Faster blocks = faster payments. But often, that comes with trade-offs in security or decentralization.
---
5. Why Blocks Matter
Blocks are what make blockchain immutable.
Because each block locks onto the previous one, you can't rewrite history without redoing all the work that came after it.
