Q. What formats are best for preserving files in the long term?
Popular formats such as those produced by Microsoft Office products (e.g. Word documents or Excel spreadsheets) are very likely to have reasonable longevity, but be aware that they are proprietary (owned by someone) and so will not necessarily exist forever or remain easily readable. It might be better to store important information in open, non-proprietary formats – for example, PDF rather than Microsoft Word, CSV rather than Excel, TIFF rather than Photoshop files, or as XML rather than a database.
However, open formats may not support all the functionality found within a proprietary format, or they might result in larger files because they offer less efficient compression of files. Sometimes, you will want to store your data in its original format and also in a more open or accessible format for sharing, archiving, or future use.
Q. What formats are best for storing files in the short- or medium-term?
Some of the best formats for ensuring that your data are available in the longer term, make it more difficult to extract or alter the raw data (e.g. a PDF versus a Word document).
If you are actively working in a format that is not good for long term accessiblity (see the answer to the question above), you should save a copy of your most important files in a long-lived format. You can do this either at the end of the project, or intermittenly.
If you are nearing the end of a project and don't have space to store multiple formats or all of your files (or time to convert them), pick your most vital files, and be sure to keep the longer access version. You may have to re-format or re-copy it later, but you will have a smaller chance of losing the information altogether.
Q. What image format should I use?
Some image formats are better for particular purposes than others. For example, TIFFs preserve digital image information well, but users cannot view them with internet browers and they take up a lot of computer storage space.
Click here to view pros and cons, along with uses for the most common image formats.
Q. What do I need to know about JPEGs?
JPEGs use something called 'lossy' compression to keep your files from being too large. This means that every time you re-save a particular JPEG file, it will lose some information. This will make your image look blurrier and blurrier over time. So, why use JPEGs at all? Answer: JPEG compression allows you to have smaller images for purposes such as web delivery and document embedding, so these are still quite useful.
For important images, or images which you may re-use, you should always keep a master copy in a non-lossy format, such as TIFF or PNG.
Q. What are 'non-proprietary' or 'open' formats, and why would I use them?
In the simplest cases, a non-properitary format is a format which does not have restrictions on its use and over which no one claims intellectual property rights. For example, Microsoft Office products, such as Microsoft Word, are proprietary, while Open Office products are non-proprietary (and open source).
For long term access to files, digital preservation experts tend to recommend 'non-proprietary' and 'open' formats. The logic here is that if the code behind the software is publically available (i.e. open source), then that format/software will be supported so long as at least one competent tinkerer still finds it interesting or useful.
In contrast, a private software company can go out of business or stop producing a compatible version of the software in whose format your data was saved, and no one will have the rights or knowledge to provide it anymore.