Saugus.net: Glossary of Computer File Extensions

Filename Extensions List

So you see a file somewhere on the 'net with a name like "greatfile.xyz" and you would like to download it and use it on your computer. Will it work? What does the file extension xyz mean, anyway? This handy guide attempts to provide answers to those questions.

It is not meant to be read straight through; rather, it is meant to be a reference. An extension may be looked up either with the "find in page" option of your browser or by appending a "#xyz" (without the quotes and with xyz replaced by the extension in question) to the "go to" or "URL" field on your browser. There is also a Search Interface that will return not only the specific extension sought but also other entries that reference it. Be aware though that it assumes familiarity with the computer basics discussed on the terms page.

You may notice that most extensions are three letters (or fewer) long. This is due to a historical limitation of the operating system called CP/M (that was later inherited by MS-DOS). In fact, the whole concept of file extensions comes from CP/M. Most modern operating systems do not attribute any special meaning to the "." (period, or dot) character.

Be aware though that there is no standardization to filename extension usage, and many different people have used extensions to apply to many different things. This list only attempts to provide likely guesses of what something is apt to be. Programs that can make use of many of these extensions can be found on the Guide to Free Software.

If you want something added or see a problem with something already here (but keep in mind this guide is not meant to be overly technical) please send .

s00 - s99: This file is designed to work on any machine that has C64 emulator software (C64 emulators are available for many platforms, including UNIX, Macs, and WinTel boxes) as well as (of course) the C64 (or C128) itself. It is essentially a repackaging of a regular Commodore sequential file.
scpt: Usually an AppleScript script, a program written in the AppleScript language. It typically runs only on Macs.
sda: A self-dissolving archive contains compressed data that should in theory decompress itself when run. The primary problem is that it will be platform specific and will only decompress properly on the same type of platform that was used to create it. Similar in principle to a self-extracting archive but different in practice. Note too that StarOffice (pre version 6.0) saves its drawing program documents with this extension; these can be read on any machine with StarOffice or OpenOffice installed (available for many platforms including WinTel boxes, Macs, OS/2 boxes, and several types of UNIX boxes).
sdc: A StarOffice (pre version 6.0) spreadsheet document; can be read on any machine with StarOffice or OpenOffice installed (available for many platforms including WinTel boxes, Macs, OS/2 boxes, and several types of UNIX boxes).
sdd: A StarOffice (pre version 6.0) presentation program document; can be read on any machine with StarOffice or OpenOffice installed (available for many platforms including WinTel boxes, Macs, OS/2 boxes, and several types of UNIX boxes).
sdw: A StarOffice (pre version 6.0) word processing document; can be read on any machine with StarOffice or OpenOffice installed (available for many platforms including WinTel boxes, Macs, OS/2 boxes, and several types of UNIX boxes).
sea: A self-extracting archive contains compressed data that should in theory decompress itself when run. The primary problem is that it will be platform specific and will only decompress properly on the same type of platform that was used to create it. Similar in principle to a self-dissolving archive but different in practice.
seb: A Franklin e-book file. It is binary and not particularly portable; in fact it is geared primarily toward dedicated e-book hardware.
seq: This is a generic sort of extension indicating a simple sequential data file. It may be either ASCII or binary, and may contain data from pretty much any character set. A file with this extension may or may not be portable. This particular extension is used heavily on C64 or C128 computers, so there is a high probability that files with it were intended for such a machine.
sfl & sfp: The SoftFont format is used for storing bitmapped fonts. It is a product of Hewlett-Packard and is supported by many HP printers. The SFL variant indicates the font is to be used in landscape orientation. The SFP variant indicates portait orientation.
sfs: The SoftFont Scalable format is used for storing vector fonts. It is a product of Hewlett-Packard and is supported by many HP printers.
sfx: A self-extracting archive contains compressed data that should in theory decompress itself when run. The primary problem is that it will be platform specific and will only decompress properly on the same type of platform that was used to create it. Similar in principle to a self-dissolving archive but different in practice.
sh: Probably a Bourne Shell script. It will work on any machine that has the Bourne Shell or Bourne-Again Shell installed.
shar & sha: Groups of files are often sharred together so that they may be handled as a single file. A file that ends with this extension is probably such a file and will have to be unsharred into its individual components before use. The whole concept of sharring started on UNIX machines, but it is also possible to get programs to shar and unshar on most other computers.
shtml & shm: An HTML file utilizing server-side includes. An SHTML file can be somewhat dynamic; a typical use is the automatic inclusion of a "last modified" date.
sid: A SID audio file is a program that will directly run on a computer with a SID chip (like a C64 or C128 or a WinTel box with appropriate hardware). As an audio format, it is fairly efficient. Furthermore, free SID players are available for most platforms, and there are even free SID playing plug-ins available for Netscape and compatible browsers.
sit: A file that has been compressed with Aladdin's Stuffit program will get the "sit" extension. It is similar in performance to gzip, but less portable. Unlike gzip, sit does not require a separate tarring step; it uses its own method to do the equivalent.
snf: The Server Normal Format is a format for storing bitmapped fonts. It is machine-dependent; that is, do not expect that a file in this format from one machine will work on another. Virtually every machine that uses SNF fonts will be able to convert them to BDF, though.
so, dll, & dylib: A shared library object (also called a dynamically loaded library or dynamic library). Whatever they are called, these things are binary and extremely platform-specific; they may fail to be usable even on two machines of the same model and OS based upon other less obvious specifics.
spd: The Speedo format is used for storing vector fonts. It originated on the X-Windows system and is a creation of the Bitstream, Inc. company.
spx: The Speex format is a binary audio format designed for holding speech. It is patent and royalty free, and is supported on most platforms.
stx: This is probably a structured text document. It is like an ordinary text document but utilizes careful structuring to indicate format.
svg: A Scalable Vector Graphics file contains XML data representing an image. It can be viewed by any application that can understand SVG data.
swf: A playable Macromedia Flash animation. Playable on any machine with the free Macromedia Flash player, currently available for (at least) Macintosh, MS-Windows, and UNIX often as a plug-in available for Netscape and compatible browsers.
sxc & stc: A StarOffice (version 6 and later) or OpenOffice spreadsheet document (they are the same); can be read on any machine with StarOffice or OpenOffice installed (available for free for many platforms including WinTel boxes, Macs, and some types of UNIX boxes). The version with the "x" is an ordinary document; the version with the "t" is a template for building other documents.
sxd & std: A StarOffice (version 6 and later) or OpenOffice drawing program document (they are the same); can be read on any machine with StarOffice or OpenOffice installed (available for free for many platforms including WinTel boxes, Macs, and some types of UNIX boxes). The version with the "x" is an ordinary document; the version with the "t" is a template for building other documents.
sxi & sti: A StarOffice (version 6 and later) or OpenOffice Impress document (used for holding presentations -- the two use the same format); can be read on any machine with StarOffice or OpenOffice installed (available for for free for many platforms including WinTel boxes, Macs, and some types of UNIX boxes). The version with the "x" is an ordinary document; the version with the "t" is a template for building other documents.
sxm & stm: A StarOffice (version 6 and later) or OpenOffice math document (they are the same); can be read on any machine with StarOffice or OpenOffice installed (available for free for many platforms including WinTel boxes, Macs, and some types of UNIX boxes). The version with the "x" is an ordinary document; the version with the "t" is a template for building other documents.
sxw & stw: A StarOffice (version 6 and later) or OpenOffice word processing document (they are the same); can be read on any machine with StarOffice or OpenOffice installed (available for for free for many platforms including WinTel boxes, Macs, and some types of UNIX boxes). The version with the "x" is an ordinary document; the version with the "t" is a template for building other documents.