File format refers to a file's type, based on its structure, layout or how it handles the information contained within it. There are many different types of formats depending on the type of file information (for example, audio files, text files or video files), and there are several different - and sometimes competing - file formats within any format type. In fact, there are over 90 different file formats for audio files and over 250 different file formats for image files.
Some file formats are designed to store very specific types of data; for example, the JPEG format is designed only to store static images. However, other file formats, can be used to store several different types of data: the QuickTime format can be used for a variety of multimedia files, whilst the GIF format supports storage of both still images and simple animations.
Most file formats are recognised by their filename extension - the section of their name following the final 'dot' or period. For example, GIF images are identified by names that end with by .gif and HTML documents by .html or .htm. Whilst the majority of filename extensions consist of three characters, they can be anywhere from one to five characters long. When the filename is double-clicked, the computer uses the file's extension to determine what program should open it.
Files may usually be opened by any program that supports that file format. Some formats may be specific to one type of software (for example, .pdf files must be opened by Adobe Acrobat); whilst others are standard formats that can be opened by any program that supports that standard format (e.g. .txt files are general text files that may be opened in any text editor or word processing program).
It is possible to change file's extension using the 'rename' option; however, as this also changes the program the computer uses to open the file, it may make a file unusable. For example, if a .txt (text) file is changed to a .doc (Word document) file, Microsoft Word will be able to open it. However, if the same .txt file is changed to a .jpg file, the file will not open.
When downloading files, it's important to have a basic understanding of file formats and extensions so that you can easily recognise the type of file when it has downloaded to your hard drive. This will allow you ensure that it is the right format for your software. For example, Windows Media Player will not play audio files with an .aac extension; you will need a copy of Apple iTunes. You will also be able to check that the file has the right format; for example, if you download an image file and you notice that its extension is .exe (an executable file) rather than a .jpg or other image format, then this should alert you to the fact that the file may actually be a Trojan horse, which could seriously damage your computer if you run it.
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