Thread: JPG or JPEG?
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Old 02-01-17, 01:31
robski robski is offline
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Join Date: Dec 2005
Location: Kent UK
Posts: 3,653

The concept of file extensions date back to the 8 dot 3 file name format used on DOS operating systems for PC. With the introduction of MS Windows 3 or (4 mainly for CAD programs) character extensions can be used. Which by default are hidden unless you override the setting. Information about the extension is held in the registry.

Although a MAC allows you to put dots in the file name for your own convenience it does not need them to know about the file. Information for a Mac file is held in 3 places. A Data fork ( the file you see on a PC ), a resource folk which contains info about the file and the thumb nail image. The file Signature which is the file type and creator is stored in the catalogue tree on the disk.

From my distant memory of when I last used Photoshop on a Mac some 15 years ago you could set what the extension was in Photoshop settings.

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