Understanding synchronization
Synchronization is a controlled way to make two folders agree. It is useful when both locations participate in a workflow—for example, a project folder on a PC and a portable working copy. It is not automatically a backup, because some synchronization modes intentionally overwrite or delete data.
Backup asks “what did this look like before?”
A versioned backup protects history. If today's file is wrong, you can return to yesterday's version. If a source file is deleted, retained restore points can still contain it. The destination is primarily for recovery, not everyday editing.
Synchronization asks “how should these folders agree now?”
A synchronization compares left and right, creates a preview, and applies the selected rules. Depending on the mode, it can:
- Copy in one direction or both directions.
- Replace an older file with a newer one.
- Carry renames and deletions to the other side.
- Combine two sets without deleting anything.
- Resolve a file that changed independently on both sides.
The same folders can produce completely different outcomes depending on the mode. Choose the intent first, then create the pair.
A simple decision guide
| Your goal | Choose |
|---|---|
| Recover old and deleted versions | Backup |
| Add/update files on the right but never remove right-side files | Copy |
| Combine everything from both folders and never propagate deletions | Merge |
| Make the right folder an exact replica of the left | Mirror |
| Work in both folders and carry all changes both ways | Two-way |
See Every mode in detail before choosing Mirror or Two-way for valuable data.
Left and right matter
In one-way modes, the left folder is the source and the right folder is the destination. Reversing them reverses the result. In two-way modes, both sides can provide changes, but conflict policies still refer to left and right.
Use names that preserve the direction, such as Laptop projects → USB working copy. Before the first run, confirm both paths in the preview.
The preview is your safety check
Before O&O AutoBackup applies synchronization changes, the preview summarizes files to create, update, move, delete, or skip. Read it as a proposed transaction:
- A high number under Removed deserves investigation.
- Unexpected changes in the opposite direction usually mean the wrong mode or reversed folders.
- A conflict means the same logical file changed on both sides since the last comparison.
Canceling the preview changes nothing. When the result is surprising, go back and correct the pair instead of approving it experimentally.
Synchronization keeps working folders convenient. A separate Backup pair preserves history when convenience propagates the wrong change.