Understand and work with file formats

A computer file can be anything from a document produced in a word processor to a photograph captured with a digital camera. However, if you have used a PC for even a short while, you will probably realise that not all files are made the same – even if they outwardly appear alike.

A Microsoft Word document, for instance, could be in one of a variety of different file formats and, if you don't have the right version of Word, you may not be able to view or edit the contents. Similarly, though most digital cameras save photos in the JPEG file format, digital images may be stored in many different formats, each with its advantages and disadvantages.

Most of the time you don't need to worry about a file's format: just double-click the file and it should open in the relevant application. But sometimes an unexpected application will be launched to display the file's contents or the file won't open at all.

In this back-to-basics guide, we will explain exactly what file formats are, how they affect the way your PC works and how to take control when strange things happen.

Why so many formats?
By now, the number of file formats runs into the thousands. Of course, you may wonder why the computing world needs so many file formats. The simple answer is that it doesn't, but over the years every software company has decided that existing file formats aren't quite right – or more to the point, not owned by them – so they invent their own, over which they have proprietary rights.

The result is an excess of file formats, many of which are little more than me-too efforts that only make life more complicated for computer users. However, for every self-interested file format there is another that exists, or has at least prevailed, for good reason.

The GIF (Graphics Interchange Format) file type, for example, was invented by an early online company called Compuserve. The GIF specification is now more than 20 years old, yet it prevails online because the limited colour palette (GIF images are made up of no more than 256 shades) and good compression leads to very small file sizes. GIF images can also be animated. This is why GIF files can still be found online today.

Format farrago
Other formats survive for less valid reasons. The DOC file, for instance, is synonymous with word-processing documents. Indeed, over the years several different word processors have used their own versions of the DOC format. These days, though, the DOC format most people know and use is a proprietary file type that belongs to, and is therefore entirely controlled by Microsoft.

Of course, Microsoft isn't committing a crime being the owner of a successful file format but there are repercussions for other software companies that wish to make applications that can read and edit DOC files.

In the early days of Word, Microsoft made it tough for other software companies to use its DOC format. As Word became the dominant word processor application it relented and allowed other companies to make their applications compatible with the DOC format, though those wishing to do so still had to gain Microsoft's permission.

More recently, Microsoft has made the DOC file format a free-for-all, so now anyone can incorporate it into a program without permission, though they still have to follow the design of the format published by Microsoft.

Microsoft also introduced a file format with the launch of Office 2007 called Officeopen XML, recognisable to users as having added an 'x' to the end of existing Microsoft file formats (so DOC files became DOCX, Excel spreadsheet files went from XLS to XLSX and so on).

The company did this openly – Officeopen XML is a free and open file format that anyone can use – but the upshot for computer users is yet more file format confusion. If you rely on Office 2003, say, and an Office 2007 user emails you a DOCX-format file, Word 2003 will not be able to open it.