Write-through and Write-back are two cache writing policies.

• Write-through updates both the cache and main memory simultaneously, ensuring consistency but making it slower.

• Write-back updates only the cache initially and writes to main memory later (on block replacement), which improves speed but adds complexity and may cause inconsistency.

Write-back uses a dirty bit to track changes, while write-through does not. Write-through is ideal for systems where simplicity and consistency matter; write-back is better when performance is the priority.