.bak vs .old: Which Backup Is Which?
Both are safety copies of a previous version, but they get created differently: a .bak is a deliberate backup, while a .old is usually the old file an installer or app renamed out of the way.
Short answer: a .bak is a backup a program made on purpose so you can roll back; a .old is normally the previous version something renamed aside before writing a new one. Both hold earlier data, and both are just the original file with a changed extension — you restore either by renaming it back.
How each is created
- .bak — editors, databases and config tools that save a backup before overwriting (e.g.
settings.bak). Meant as a rollback point. - .old — installers, updaters and system tools that rename the current file to
name.oldbefore dropping a new one in. It is the leftover previous version.
Which should you restore?
To undo a recent change, restore the copy whose timestamp matches the version you want — check the file dates, not just the extension. Rename it back to the original name (remove .bak/.old) after moving the current file aside. Keep a .bak while you are actively editing; a .old left by an update is safe to delete once the new version works.
FAQ
What is the difference between a .bak and a .old file?
A .bak is a backup a program saved on purpose so you can roll back. A .old is usually the previous version something renamed out of the way before installing a new one. Both contain earlier data.
How do I restore a .bak or .old file?
Move or rename the current file aside, then rename the backup by removing the .bak or .old extension so it becomes the original filename again.
Can I delete .old files?
Yes, once the new version works correctly. A .old is a leftover previous copy; keep it only if you might need to roll back.