Storage vs memory vs calldata in Blockchain / Solidity - Visual Side-by-Side Comparison

Concept Flow - Storage vs memory vs calldata

Function Call

↓

Parameters Passed

↓

Calldata (Read-only, cheap)

↓

Memory (Temporary, modifiable)

↓

Storage (Persistent, expensive)

↓

Function Execution

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End of Execution

When a function is called, inputs come as calldata (read-only). Data can be copied to memory (temporary, modifiable). Storage holds persistent data on blockchain, which is expensive to read/write.

Execution Sample

Blockchain / Solidity

contract Example {
  uint storedData;
  function setData(uint x) public {
    uint temp = x; // memory
    storedData = temp; // storage
  }
}

This contract sets a stored value by copying input from calldata to memory, then to storage.

Execution Table

Step	Variable	Location	Value	Action
1	x	calldata	5	Function called with input 5
2	temp	memory	5	Copy x from calldata to memory
3	storedData	storage	5	Write temp value to storage
4	-	-	-	Function execution ends

💡 Function ends; calldata is discarded, memory cleared, storage keeps value

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
x (calldata)	-	5	5	5	-
temp (memory)	-	-	5	5	-
storedData (storage)	0	0	0	5	5

Key Moments - 3 Insights

Why can't we modify calldata variables directly?

Calldata is read-only as shown in step 1 of execution_table; to modify data, we copy it to memory (step 2).

Why is storage more expensive than memory?

Storage persists on blockchain and costs gas to read/write (step 3), while memory is temporary and cheaper.

What happens to memory and calldata after function ends?

Both calldata and memory are cleared after execution (exit_note), only storage keeps data.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'temp' after step 2?

A -

B 0

C 5

D Undefined

💡 Hint

Check the 'Value' column for 'temp' at step 2 in execution_table

At which step is the value written to storage?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for when 'storedData' changes

If we tried to modify 'x' directly, what would happen?

A It would cause an error because calldata is read-only

B It would modify calldata successfully

C It would modify storage instead

D It would modify memory automatically

💡 Hint

Refer to key_moments about why calldata is read-only and step 1 in execution_table

Concept Snapshot

Storage vs Memory vs Calldata in blockchain:
- Calldata: Read-only input, cheapest, temporary
- Memory: Temporary, modifiable during function
- Storage: Persistent, expensive, saved on blockchain
Copy calldata to memory to modify; write to storage to save permanently.

Full Transcript

When a blockchain function is called, inputs come as calldata, which is read-only and cheap. To change data, we copy it to memory, which is temporary and modifiable during the function. Storage holds data permanently on the blockchain and is expensive to read or write. In the example, input 'x' is received in calldata, copied to memory as 'temp', then saved to storage as 'storedData'. After the function ends, calldata and memory are cleared, but storage keeps the data. This flow helps manage cost and data persistence efficiently.