Putting an extension on a filename

marmaduke | 10:53 Mon 15th Nov 2004 | Technology

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Why does putting an extension like like .jpg or .doc make the file suddenly readable if it hadn't been before? Why doesn't the computer know what it is if a paint program, for example, saves a file only as 'picture' and not 'picture.jpg'

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j2buttonsw

Microsoft use file extensions so they can associate different file types with different applications. For instance document.doc is associated with Word as .doc files will cause Word to open. If I had simply document you would need to go through all applications you have installed on your PC to view it.

booksworth

The computer _ought_ to be able to tell what kind of file it is without an extension, because lots of different file type definitions require a few bytes early in the file to say what kind of file it is. (An obvious example is <HTML> at the beginning of a web page.) Sadly, this subtlety seems to have escaped Microsoft.

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