These three words get used interchangeably, and the confusion is expensive. Each is a distinct tool with a distinct job, and substituting one for another produces a specific and predictable failure.
The three definitions
Sync keeps multiple locations identical. Change something in one place, it changes everywhere. Its job is access — having your files current on every device.
Backup keeps copies of how things were, separately from the live copy, so you can go back. Its job is recovery — getting something back after it's lost or damaged.
Archive moves things you're finished with out of the way, to somewhere cheaper or slower, for long-term keeping. Its job is retention — holding onto material you rarely need without letting it clutter or cost.
The three questions that tell them apart
1. If I delete the original, what happens to the copy?
Sync: it's deleted too, within seconds. Backup: it survives, until the retention period ends. Archive: there is no original — the archive is the copy.
2. Does it keep history?
Sync: a little, via version history, for a limited window. Backup: yes, that's the point. Archive: no. An archive holds one version — the final one.
3. How often do I read from it?
Sync: constantly. Backup: almost never, and urgently when I do. Archive: rarely, and without urgency.
What each is actually for
Sync
Your working files, available everywhere, always current. Cloud storage services, and any two-way folder synchronization.
Good at: working across devices, collaborating, not carrying a laptop everywhere, surviving hardware failure.
Bad at: protecting you from yourself. Deletion, overwriting, corruption, and ransomware all propagate faithfully. Version history and trash give you a limited window, and that's all.
The failure: "everything's in the cloud so I'm backed up." Then a folder gets deleted, nobody notices for four months, and the retention window closed three months ago.
Backup
A separate copy, with history, that doesn't mirror your mistakes. Backup software to an external drive, or a dedicated cloud backup service.
Good at: recovering from deletion, corruption, ransomware, hardware failure, theft, and mistakes discovered late.
Bad at: being convenient. Backups aren't browsable the way a folder is, restores take time, and nobody enjoys maintaining them.
The failure: setting one up and never testing it, or letting the drive stay permanently connected so ransomware reaches it too.
Archive
Finished material, moved somewhere out of the way. An external drive of completed projects, a cold storage service, a box of labelled disks.
Good at: keeping your active storage small and navigable, reducing subscription costs, and satisfying retention obligations.
Bad at: protecting anything. An archive is not a backup, because an archive typically holds the only copy. If the archive drive dies, the material is gone.
The failure: treating an archive as protection. "I moved it to the archive drive" is not "it's safe." An archive needs its own backup — two copies of the archive, ideally in two places.
The most consequential confusion: archive is not backup
This one deserves its own section because it's the least obvious and the most damaging.
People diligently move finished work off their main drive onto an archive drive, feel organized, and delete the originals. The archive drive now holds the only copy of years of work, sitting in a drawer, unread and unverified, on hardware that will eventually fail.
Rule: an archive needs at least two copies, in two places, and periodic verification.
Two drives, one at home and one elsewhere. Or one drive plus a copy in cold cloud storage. And plug them in once a year to confirm they still read — drives that sit unused for years develop problems, and you find out when you need them.
How they work together
A complete setup uses all three, each for its own job:
ACTIVE WORK
Synced across devices (cloud storage)
Backed up with history (external drive + cloud backup)
FINISHED WORK
Archived off the main drive (external drive)
Archive itself duplicated (second drive, off-site)
THE IRREPLACEABLE CORE
In all of the above, plus a separate copy
somewhere independent of any one accountThe flow of a file over its life: it's created in synced storage, backed up continuously while it's active, and archived when it's finished — with the archive itself duplicated.
Where common tools sit
Cloud storage services — sync. Some have backup-like features (version history, trash retention, point-in-time restore on business tiers), but their core behaviour is sync.
Cloud backup services — backup. A different product category, designed for retention and restore rather than access.
Built-in operating system tools — backup, with version history.
Bootable clones — a hybrid: a current copy of your whole disk, usually without history. Excellent for immediate recovery from a dead machine, weak for recovering something you deleted last month, because a clone that runs after the deletion contains the deletion.
Cold and object storage services — archive, priced accordingly. Cheap to store, sometimes charged to retrieve.
A NAS or network drive — depends entirely on how you use it. A NAS you sync to is sync. A NAS you back up to is backup. A NAS holding your only copy of finished work is an archive, and needs its own backup.
Phone cloud backup — genuinely backup. Point-in-time device snapshots.
Photo sync in a cloud photo service — sync, not backup, despite being widely believed otherwise.
The one-line test
For anything you're relying on, ask: "If I made a terrible mistake right now, would this copy still have the good version tomorrow?"
Yes → it's a backup. No → it's sync. There is no other copy → it's an archive, and it needs a backup.
The practical takeaway
Have all three, deliberately. Not one thing you hope covers everything.
Don't let sync be your only protection. It handles one class of disaster very well and several others not at all.
Give your archive a backup. The thing you're least likely to notice failing is the thing you never open.
Test the backup. Sync tests itself constantly by virtue of being used. Backups and archives do not, which is exactly why they fail quietly.
Most people reading this already have sync. The gap is usually backup, and the invisible gap is usually the archive.
Next in this series: What to Do the Day Your Hard Drive Dies