File Extension is a three-digit designation at end of a file name that tell the computer what format the file has been saved in. (Examples: .doc, .txt, .pdf, .psd) Each different type of file has a different file format. A file format specifies how information is organized.
Filename extensions were used in Digital Equipment Corporation (DEC) operating systems (for example, TOPS-10, OS/8 and RT-11). CP/M adopted the convention and MS-DOS, as a re-implementation of CP/M, did so as well.
The DEC operating systems internally split the filename into a "base name" and a filename extension, with the "base name" limited to five to eight characters (initially nine in RSX and VMS) and the extension limited to two or three characters; when a filename/filename extension combination was typed in commands, a dot (.) was placed between the filename and filename extension. CP/M worked the same way; the filename was limited to eight characters and the filename extension was limited to three characters, with a dot between them. Early versions of the FAT filesystem used in MS-DOS and Microsoft Windows imposed the same limitations. This is sometimes referred to as the 8.3 filename convention, and since the word filename is eight letters long and ext is a reasonable abbreviation for extension, it can be generalized as:
FILENAME.EXT
The filename extension was originally used to easily determine the file's generic type. The need to condense a file's type into three characters frequently led to inscrutable extensions. Examples include using .GFX for graphics files, .TXT for plain text, and .MUS for music. However, because many different software programs have been made that all handle these data types (and others) in a variety of ways, filename extensions started to become closely associated with certain products—even specific product versions. For example, early WordStar files used .WS or .WSn, where n was the program's version number. Also, filename extensions began to conflict between separate files. One example is .rpm, used for both RPM Package Manager packages and RealPlayer Media files; others being .qif, shared by DESQview fonts, Quicken financial ledgers, and QuickTime pictures, and .gba, shared between GrabIt scripts and Game Boy Advance ROM images.
People often have a belief that file extension problems are quite normal, but they do not know that these problems generally occur due to the registry. Many a times it happens that a software necesarry to run a particular kind of file extension is already present in the computer but it may happen that the registry looses this information and the program does not function properly. For checking these registry errors and repairing them some softwares are availlable which are very necessary to have in the computer.
