What Are File Extensions

File formats are generally not something you ever worry about. You receive an e-mail with an attachment, you double click, and hey presto your PC opens it using the appropriate software. The way in which a PC does this is through the use of file extensions, the three or four letters and numbers that come after the full stop in the filename. Most computer users are familiar with the most common file extensions such as .doc (Microsoft Word) or .mp3 (Music File). Modern computers can run countless software applications using thousands of different file extensions all of which need to be identified by the computer in order for them to work correctly.

File designations consist of two parts; a file identifier and a file extension. The identifier is the part that’s useful to users and allows us to attribute a useful name to the file such as ‘Accounts’ whereas the file extension is required by the operating system to identify which application it requires to open a file.

In the early days of computing users were generally familiar with file extensions as they were constantly visible when searching your computers storage. Files were limited to what was known as an 8.3 file-name which limited the file identifier to 8 characters and the file extension to 3 characters. The problem with this system was it was all too easy for novice users to accidentally change the file extension when renaming files and suddenly the operating system nor application recognise the file.

As operating systems became more sophisticated they were able to hide the file extension by default whilst still allowing more experienced users to view this information if required. File identifiers also became longer and more user friendly allowing spaces between words. These days when most users trawl through their hard drives they no longer see the file extension but simply the file-name. This however does create an issue when two files share the same file identifier such as two files about accounts such as ‘Accounts.doc’ and ‘Accounts.xls’ ( a Microsoft Word file and an Excel Spreadsheet). These two very different files both appear as ‘Accounts’ when viewed in a list. This has now largely been solved with the greater user of graphical interfaces where each file format has its own icon that users quickly get to know and therefore do not confuse text documents with spreadsheets.

These days file extensions rarely trouble the user however at some point most users will experience the ‘Unknown file type’ error. This is when the operating system then turns to the user to ask for help in identifying which application it requires to access the file. Thankfully with the advent of the internet and file extension databases most operating systems are able to retrieve the information without user input and advise if additional software is required.

With increasingly user friendly graphical interfaces and file names the humble file extension is largely a mystery to most users but without these 3 or 4 characters your PC and most users would be unable to ‘open file’.