How GBM AI finds the files that changed
Each backup saves only what changed. How GBM AI tells which files those are, why it never uses or touches the Windows archive bit, and why another backup program does not get in its way.
On this page
After the first full backup, each backup saves only the files that are new or have changed. This page explains, in plain words, how GBM AI tells which files those are.
In short#
- GBM AI compares each file with what the last backup recorded about it. It does not use the Windows archive bit.
- It never changes the archive bit, or any other setting, on the files it backs up. A backup only reads your files.
- Continuous jobs do not even need to look: Windows tells them what changed.
How a scheduled backup decides#
For every file it saves, GBM AI keeps a short record in the backup: the file's size, when it was last changed, and a fingerprint of its contents. At the next backup it compares each file on your PC with that record, and saves the file again when:
- its size is different;
- its last-modified date is different;
- Windows' own change stamp is different. NTFS and ReFS drives, which is nearly every Windows drive, keep one for every file. It catches a program that changes a file but puts its date back, as encrypted containers do;
- it was made read-only, hidden or system, or no longer is;
- or GBM AI cannot tell for sure. Saving the file again is the safe answer; skipping it is not.
Opening a file to read it, a virus scan, or copying it somewhere else does not make it count as changed: none of them alter what GBM AI compares.
Files kept in OneDrive, Dropbox or iCloud are judged by their size and date only, because the sync app moves their change stamp itself each time it downloads them or frees their space.
How continuous protection knows#
A continuous job (Pro and Server) is told what changed, so it never has to look through every folder:
- on an NTFS or ReFS drive, Windows keeps a list of every change (the change journal), and GBM AI reads it;
- on a drive without one, such as an exFAT or FAT32 USB drive, GBM AI watches the folders while it runs;
- a network share is looked at every 15 minutes.
See Continuous protection for the details.
The archive bit#
Every file in Windows has an archive setting, which Windows switches on whenever the file is written. Older backup programs, and commands such as xcopy /M, use it as a to-do list: they back up the files that have it on, then switch it off.
GBM AI works differently:
- It never switches the archive bit off, or changes it in any way, on the files it backs up.
- It does not use the archive bit to decide what to back up, so it misses nothing when another program switches it off.
- When you restore a file, it gets back the settings it had when it was backed up, the archive bit included (while Restore dates and attributes is on, as it is unless you change it).
So GBM AI can run on the same PC as another backup program that relies on the archive bit. Neither gets in the other's way.
Common questions#
I use another backup program that clears the archive bit. Will GBM AI miss files?#
No. GBM AI does not look at the archive bit, so whatever another program does to it makes no difference.
Will GBM AI make my other backup program miss files?#
No. GBM AI leaves the archive bit exactly as it finds it. A program that relies on it sees the same files it would have seen without GBM AI.
A program changed a file but kept its date and size. Is the change backed up?#
On an NTFS or ReFS drive, yes: Windows' change stamp moves whatever the program does with the date. On a USB stick or memory card formatted exFAT or FAT32, which keep no such stamp, GBM AI goes by the size and the date.
Why was a file I did not touch backed up again?#
Something else wrote to it: a program that saves a file when it opens it, a sync app, or a tool that updates dates. Its date or its change stamp moved, so GBM AI saved it again rather than risk missing a change.