Slots and Blocks on Solana — Why You Can’t Think Like EVM

If you’re coming from EVM chains (Ethereum, Base, BSC, etc.), it’s very tempting to map Solana concepts 1:1 to what you already know.

That’s where a lot of misunderstandings start.

On Solana, slots and blocks are not the same thing — and treating them like Ethereum blocks will give you wrong assumptions about time, ordering, and data completeness.

Let’s break it down.

1. What Is a Slot on Solana?

A slot is a logical unit of time in Solana: ~ 400 ms per slot
Each slot has a designated leader
The leader may produce a block during that slot
Key point:
- A slot does NOT guarantee a block.
- Some slots are: Empty, Skipped, Or produce partial data that never becomes finalized

So:

Slot ≠ Block

2. What Is a Block on Solana?

A block only exists if the leader successfully produces one for that slot.

A Solana block:

Is associated with exactly one slot
Contains:
- Transactions
- PoH entries (hashes)
Has:
- blockTime
- blockHeight

But:

 - ❌ Not every slot has a block
 - ❌ Slot numbers are continuous, block heights are not

Sample slot without block
https://solscan.io/block/397551930

This already breaks a common EVM assumption.

3. Compare This to EVM Blocks

On Ethereum-style chains:

 - Time is organized by blocks
 - Each block:
         - Advances state
         - Has a parent
         - Has a timestamp
 - No concept of “empty time units”
 - Simplified EVM model:

         - time → block → state

Solana model is closer to:

 - time → slot → (maybe) block → state

4. Finality and Reorgs Feel Different

Another big mental shift:

EVM - Blocks may reorg - Finality is probabilistic (or epoch-based)

Solana
- Slots are always advancing
- Blocks can be:
- Produced
- Dropped
- Replaced before finalization

 - This means:
         - You may see a block at a slot
         - Then later that block is no longer part of the finalized chain
         - If you index Solana data, you must care about commitment levels: processed, confirmed, finalized