I have family photos that go back more than 100 years. But I can't be sure that, a hundred years from now, my descendants will have my photos.
No one knows for how long your files will be accessible. Both file formats and physical media can go out of fashion. And the media itself may not be stable over the long haul. I can't guarantee anything, but these steps will increase the odds that your descendants can know their ancestors.
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1. Pick file formats with staying power
Think about the formats in which you should save your archival files. Select open formats that are widely used and readable by many current programs. For instance, programs that can display JPGs will probably be around longer than ones that support camera-specific RAW files.
Other good formats include PDF, DOCX, MP3, MP4, and MOV. If possible, save and store the same files in multiple formats.
2. Don't encrypt
You need to encrypt your credit card information and your passwords, not your family photos. It will be hard enough for your descendants to find and open the files without looking for a long-lost password.
3. Store archival files on your main drive
Whether it's a hard drive, an SSD, or something not yet invented, keep your files on the main storage unit inside your computer. When you upgrade to a new drive or a new PC, you'll want transfer all your data--including your archival files. That provides insurance against the degradation or loss of the older drive.
4. Set files to read-only
Designating files as read-only adds a layer of protection against accidentally deleting or overwriting precious data.
To make your archival files read-only in Windows, right-click the folder containing them and select Properties. Check Read-only. Clicking OK or Apply will bring up another dialog. Select Apply changes to this folder, subfolders, and files.
5. Make your archives part of your regular backup
Back up regularly, and make sure that the folders containing archival material are part of the daily routine. If you don't have a regular backup routine, now would be a good time to start.
6. Burn files to optical discs, but choose the right discs
CDs, DVDs, and Blu-ray discs have some serious archival advantages. They're write-once, so you can't accidentally erase or overwrite a file. And you can make multiple copies cheaply and easily, sending them out to family and increasing the odds that one disc will survive.
Most writable optical discs aren't very stable, unfortunately. They could all be unreadable in a few years.
Instead, I recommend you use M-Discs. I don't trust the claim that they'll last 1,000 years, but tests have proven them far more resilient than other discs. You'll need a drive that supports M-Discs to burn them, but any drive can read them.
Will your descendants have optical drives Probably not. But if enough people archive this way, the drives will be available, even if you have to go to a specialist to use one.
7. Make sure loved ones know about these files
If no one knows about them, no one might ever see them.