Does online update computer folder or visa versa?

[Yofi]

I had a PC hard drive crash. Windows 10 disk wouldn't fix it so I hooked up my secondary drive to get it to boot. This drive has a backup Dropbox folder that I had made earlier. When I got original boot drive working it now shows the older folder and so does website. I'm assuming that as soon as I started the older drive it updated online to this older folder and when I got the original drive to boot the website updated the folder on the PC. So does the PC Dropbox folder update the website or does the website update the computer folder?

[Rich]

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So does the PC Dropbox folder update the website or does the website update the computer folder?

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Neither. Any change is synced, in either direction. Even if you replace a newer file with an older one, Dropbox sees it as a change and will sync it. Do not assume that just because a file is newer that Dropbox will sync the new one replacing the old one. It all depends on the order of the events, not the time stamp of the file.