Data Rot: Or Why You Shouldn’t Put Flash Drives in Time Capsules

Over a decade ago, I heard about scientists making sapphire disks that you could print on like microfilm, meaning that in some post-apocalyptic future, so long as you could make rough glass lenses (a 17th-century technology, and one that could also probably be described on another disk alongside those microfilms in a more-easily readable format). Several years ago I first heard about Project Silica, a Microsoft research project to store massive amounts of data on special glass plates, like a massive CD-R. Neither technology is at the place where you can buy it yet, but I’m hopeful it’ll get there someday soon.

The idea of a storage medium that could survive millions of years was awe-inspiring, and also inspired a sense of terror in me. I remember hearing offhand about some CD-Rs dying after only a few years because the film stopped sticking to the disk, meaning that it was unreadable. I had roughly 50+ CDs and DVDs that I had burned starting in the 90s as a backup solution. I started ripping all of them to my server storage and found many instances where data was already missing, less than 25 years later.

If you’re storing your data on a medium that isn’t literal stone or glass, it’s not permanent!

Magnetic, spinning hard drives and floppy drives store data by magnetizing different metal parts on the disk. If left untouched, magnetic charges across the disk will start to cancel each other out, making it harder for a computer to read the data. This can take a long time, probably a few decades, and it’s more likely that in the meantime a physical component will wear out.

Commercial DVDs and CDs have data written as carved-out pits in the plastic layer next to a reflective film, while writable ones use a dye that changes colors when heated, creating the same pattern. In either case, the “top” side of the disk is the more delicate side, as anything that scratches off the reflective coating will make it unreadable. This will happen anywhere between 20-50 years for writable disks to 50-100 years for mass-produced ones (provided you don’t scratch them!).

That leaves the most recent advancement in storage: Flash Memory. Flash memory is made up of many tiny little cells that are separated from each other electrically. When you write data to them, you push a larger current into that cell, which pushes a charge into it that then stays there. Another part of the circuit can detect if there is a charge in a cell, and what the charge level of a cell is, allowing data to be read very quickly. Unfortunately, those charges degrade over time. Most modern drives have a controller that checks that and tops up any low charges. However, if you’re leaving it unplugged, it can go bad fairly quickly, often within a few years.

So, if you’re thinking about making a time capsule and want to put in some old photos, maybe spend a little extra money and print them on good photo paper.