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

Concept Flow - Storage vs memory usage

Start Transaction

↓

Check Data Type

↓

Storage

↓

Write to Disk

↓

Cost Gas

↓

End Transaction

This flow shows how blockchain handles data: deciding if data goes to storage (permanent, costly) or memory (temporary, cheaper).

Execution Sample

Blockchain / Solidity

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

This smart contract stores a number permanently and uses a temporary memory variable inside a function.

Execution Table

Step	Action	Variable	Location	Value	Gas Cost Impact
1	Function set called with x=5	x	Input	5	No
2	Assign x to storedData	storedData	Storage	5	Yes (high)
3	Assign x to temp	temp	Memory	5	No (low)
4	Function ends, temp cleared	temp	Memory	cleared	No
5	storedData remains	storedData	Storage	5	Stored permanently

💡 Function ends, memory variables cleared, storage variables remain with gas cost paid

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
x	undefined	5	5	cleared	cleared
storedData	0	5	5	5	5
temp	undefined	undefined	5	cleared	cleared

Key Moments - 3 Insights

Why does storedData cost gas but temp does not?

Because storedData is saved in storage which is permanent and costly (see step 2 in execution_table), while temp is in memory and temporary (step 3 and cleared at step 4).

What happens to memory variables after function ends?

Memory variables like temp are cleared after the function finishes (step 4), so they do not persist.

Can storage variables be changed without gas cost?

No, changing storage variables costs gas because it writes to the blockchain permanently (step 2).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of storedData after step 3?

A cleared

B undefined

C 5

D 0

💡 Hint

Check the 'storedData' row after step 3 in variable_tracker.

At which step does the memory variable temp get cleared?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'temp' variable value change in execution_table and variable_tracker.

If storedData was assigned inside memory instead of storage, what would happen to gas cost?

A Gas cost would be zero

B Gas cost would increase

C Gas cost would stay the same

D Gas cost would be unpredictable

💡 Hint

Refer to gas cost impact in execution_table for storage vs memory assignments.

Concept Snapshot

Storage vs Memory in blockchain:
- Storage: permanent, costly, saved on blockchain
- Memory: temporary, cheap, used during function execution
- Writing to storage costs gas
- Memory cleared after function ends
- Use storage for data to keep, memory for temporary calculations

Full Transcript

This visual execution shows how blockchain smart contracts handle storage and memory. When a function runs, input variables are received. Assigning a value to a storage variable saves it permanently on the blockchain and costs gas. Assigning to a memory variable uses temporary RAM and costs little or no gas. After the function finishes, memory variables are cleared, but storage variables remain. This distinction is important because storage is expensive and permanent, while memory is cheap and temporary. The execution table traces each step, showing variable values and gas cost impact. Key moments clarify why storage costs gas and memory does not, and what happens to variables after function ends. The quiz tests understanding of variable states and gas costs. The snapshot summarizes the main points for quick review.