Reader Kirk Edgar has a question for the ages. He writes:
I'm in the process of cleaning out my iMac--removing data that's not current and apps that I don't use or won't work under Yosemite. Because I've done this before and been stuck with unreadable media, what's the best way of archiving digital material so that it can most likely be retrieved in the future if desired?
Given that my prophetic powers are no more honed than the average guy who writes on the Internet, I can't, with absolute certainty, tell you which formats will and won't survive. But I can offer some guidelines.
For archived files, stick with popular formats
You need spend only five minutes with a dedicated AppleWorks user to get a hint of how painful it can be to lose files because their format has been relegated to the dustheap. Much as you may prefer working with App X, if it's a not-terribly-popular app and it saves files in a proprietary format, you could be looking at trouble down the road. At the very least, when saving files and presented with the option to make an additional copy in a popular format, seize it. This may not result in a file as editable as you may like, but at least you have some kind of copy that you can work with at a later date.
I'm not suggesting that you delete any original files. They still work and may continue to. I'm simply saying that having a copy in a different (and popular) format can't hurt.
Keep an eye peeled
Again, sorry to twist the knife, but there were plenty of signs that ClarisWorks/AppleWorks file formats were going the way of the dodo long before they vanished entirely. Apple stopped updating AppleWorks, which should have hinted that it was time to move on. In those days you could still convert many (though not all) ClarisWorks and AppleWorks files to common file formats with relative ease, using tools such as DataViz's MacLinkPlus Deluxe.
Yet even with these hints, many AppleWorks users stubbornly continued to create files that were soon to be obsolete. By the time these folks accepted that their beloved application suite was well and truly dead, it became that much harder to convert their files, as the necessary tools became unavailable or incompatible with the modern Mac OS. Don't be that person.
Trust the government (and others)
When considering the best formats to use for your media and files, take a look at the formats adopted by large corporations and governments. For example, the vast majority of online forms are saved as PDF files. While Microsoft may change the way Word files are saved (and heaven knows we've seen changes in Apple's iWork formats), PDF looks like the solid bet for preserving formatted text. And plain text has been around forever and I can't image that it won't be for years to come. It's not formatted, but at least it's readable.
In regard to media, you want to look for formats that are both popular as well as unmucked-with.
Images. For example, when archiving images I might choose to keep both the original raw files as well as JPEG copies. With the former I'll hopefully continue to have access to all the data the original image contained. With the latter--because it's such a popular format--there's every chance that I'll be able to view that image decades from now. (If I wanted to be doubly careful I might make an uncompressed TIFF copy of important images.)
Audio. For audio files you can look at AIFF and WAV, which are both popular and uncompressed. MP3 isn't going anywhere anytime soon, but it is a compressed format. Apple Lossless sounds great, but it's a format largely restricted to Apple devices.
Video. When we talk about video, we're thinking of your personal movies rather than commercial releases. (Don't worry, even into the 24th century, Disney will find a way to sell our bunker-dwelling descendants cave-painted copies of The Lion King.)
Check Google for the most common movie file types and you'll find the first hit lists Windows Media, QuickTime, Real Media, MPEG, DIVX, and Flash formats. That may have been a lovely list when it was first put together, but if you know anything about movie files you're chuckling right about now. Some of these formats are all but dead and others will be soon enough.
At this particular point in time MPEG-4 (particularly the H.264 varient) looks like the best bet as it's widely used for streamed and downloaded video as well as for Blu-ray discs. It's typically a lossy format, but high bit rate files can look amazing. Fortunately, you needn't make a decision right now. Keep your original files in the format you prefer--QuickTime, for example. As you see standards change, consider creating copies in the flavor of the decade.
You can't preserve what's not there
Something else to consider is how you back up your data. It's all well and good to create copies of it in forms likely to work on into the next several decades, but if the device or service you've archived it to gives up the ghost a year or two from now, then where are you? It's for this reason that you should have redundant backups of the files and media most precious to you. For now, that means hard drives and online storage. (And hey, what's wrong with printing your images and text?) If you're really serious about this, I urge you to read Rob Griffiths' The Paranoid Person's Guide to a Complete Mac Backup. Implementing his entire workflow is overkill for... well, just about anybody. But it offers some great backup strategies.
Finally, there's perspective
At the risk of unearthing a painful personal memory, a couple of years ago my child and I stood before my vinyl collection while I proclaimed, with a magnanimous sweep of my arm, "Some day this will all be yours!"
To which my spawn replied, "I will bury them with you."
And that about sums it up. Precious though you may believe your every image, movie, and file, there's a good chance that some of them need not be preserved. Culling your stuff now (rather than leaving it to others) will make managing your remaining data easier.