Understanding File Formats

FAQ: I’m trying to exchange files with my friend but it’s not working. Do I need to just give up and buy a different computer or program?

A: Perhaps, but first it would help to understand the situation better, to understand what you are doing and how “file formats” work on modern computers.

Back in the forties when I was a boy there was basically one file format: paper. Sure, some weird recluses would keep these odd round things they called “records” or “LP’s” and the technicians at the theaters had this strange string they called “film” but essentially everything we dealt with was paper. We had certificates printed on paper, and paper kept in books, there were index cards of paper and file cabinets full of the stuff. Sometimes pictures were printed on special, shiny “photograph paper” but essentially it was all kind of foldy and flat and didn’t like to get wet much, or else it would get moldy. Exchanging files back and forth pretty much consisted of not losing them and hoping that the other person could read.

Oh, how times have changed.

At a very fundamental level, everything on your computer is ultimately made up of a collection of ones and zeroes, much as your body is mostly made up of water and carbon. What makes the computer (or your body) able to do the complex variety of things it does, however, are higher level organization that converts those two digits to letters and symbols and words and commands and things which can be read and displayed using programs. In the Unix or DOS world, programs are sometimes called “binaries” or “executable” files, because they are loaded into RAM and executed as instructions. Other files are simply written, holding their data in a prescribed structure. This structure is what we mean by “file format” and each program has a limited set of file formats that it can understand.

Most everyone understands the difference between a plain text document, a spreadsheet, a photograph and a web page. Most people also understand that some programs can read and work with these kinds of documents and some cannot. No matter how fancy your camera is, you cannot point it at a pile of goods and click to create an inventory list (yet). Each program has file formats that it prefers to work with and other formats that it CAN work with to some extent or another. These first formats are said to be a program’s “native formats” while others are sometimes called “exchange formats.” Microsoft Word’s native format, for example, is the “.doc” format first used in Word 97, but it can import and export (more or less) from a much wider variety.

Fortunately, you do not need to have the program that created a file in order to read or work with it, so long as you have SOME program that can understand the file format. The JPEG format, for example, can be read by literally hundreds of different programs, as can many other file types, often making them the best choices for archives or data exchange.

Identifying Formats

Most modern computers use “file suffixes” to label the format of a file. The suffix (or “extension”) is the last few letters of a file’s name, usually preceded by a period or “dot.” Because DOS file names were restricted to the “eight dot three” rule of file names no longer than eight characters and suffixes no longer than three, most of these suffixes are three letters or have three-letter equivalents. Most of the time identifying a file format is no more complicated than checking the file’s suffix, so if someone sends you a file you cannot open, begin by looking there.

Some of the more common file formats (listed alphabetically) include:

  • .aac – Another sound format, used by Apple’s iTunes
  • .ai – Adobe Illustrator format for vector graphics
  • .aif – AIFF format for sound files, also used on music CD’s
  • .bat – DOS batch file, usually a virus or malware
  • .csv – Comma-separated value, also used for data exchange
  • .cwk – ClarisWorks or AppleWorks document
  • .dmg – Macintosh OS X disk image file, usually an installer
  • .doc – Microsoft Word word processing format
  • .eps – Encapsulated postscript, usually for high-end graphics
  • .exe – Windows executable, usually a virus or malware
  • .gif – GIF graphic, usually used for web graphics, animations
  • .hqx – Macintosh file compressed using the binhex format
  • .htm – HTML web page, the native language for most web pages
  • .jpg – JPEG photograph, usually used for pictures
  • .m4p – Protected AAC file, used by iTunes music store
  • .mov – Quicktime format, usually audio and/or video
  • .mp3 – MP3 format, used for sound files and music players
  • .pdf – Portable Document Format, electronic forms for printing
  • .ppt – Microsoft PowerPoint slideshow
  • .psd – Adobe Photoshop document
  • .rm.ram – RealPlayer media, audio file for RealPlayer
  • .rtf – Rich Text Format, a simpler word processor interchange format
  • .scr – Windows screensaver, usually a trojan horse or malware
  • .swf – Flash animation, used for web animations and games
  • .tab – Tab-delimited text, frequently used to exchange data
  • .tar – Tar-compressed file
  • .tif – TIFF format for raster graphics, also used by faxes
  • .txt – Plain old ASCII text, a venerable standard
  • .vbs – Windows visual basic script, usually a virus or malware
  • .wav – WAV format, used for computer sounds
  • .wma – Windows media audio file, used for Windows audio
  • .wmv – Windows media video file, used for online movies
  • .wpd – WordPerfect word-processing document
  • .wps – Microsoft Works word-processing document
  • .xls – Microsoft Excel workbook format, for spreadsheets
  • .zip – Zip-compressed file, will usually expand to a folder

Attachment Etiquette

There is a tendency among new computers especially to assume that everyone’s computer is exactly the same as theirs, and that if they (a naive user) can work with or see a file then anyone else can, without question. This is why it is a habit among seasoned computer users to ask before sending an attachment or file, if possible, or at least to describe the attachment in the body of the email or in a little “about.txt” file somewhere in the folder or disc. It is amazing how much time and frustration it saves to include a simple sentence such as “Enclosed please find compromising photos of the senator, as three JPG files compressed into a Zip file.”

When you cannot read an attachment, you might use the chart above to begin searching for a program to open a given file, or you might ask the person to resend the information in another format. Usually they do this from their program’s “File” menu by looking for a command such as “Save As…” or “Export.” If they get upset about this, it is probably because they do not know how, so it is usually best to be patient with them and help them learn. Some programs are roach motels that bring in data but don’t let it to, in which case it may be easiest over the short term to “print” a PDF of the data or take a screenshot to send along instead. As a good citizen, it behooves you to learn how to do this yourself, so that you can export data from each of your main programs: word processing, database, graphics, etcetera. Creating a PDF under Mac OS X is as easy as going to print a file and then (from the confirmation dialogue) clicking on the “Save as PDF” option. Pretty much anyone can download the free Adobe Reader and view a PDF. To zip compress a file in OS 10.3 or higher, hold down the “control” key as you click on the folder in the Finder and select the option to “Make an Archive.”

Don’t Despair

There is a reason that lots of sophisticated users hate email attachments, and for Windows users especially it is a good idea NOT to try opening every attachment you receive, especially if it ends in one of the dangerous suffixes such as “.exe” or “.vbs”

For those who work a lot with files of different sorts there are programs which specialize in moving data between and amongst them. The most common and popular among Mac users come from a company called Dataviz and are called “Mac Links Plus” (for the Mac) and MacOpener or Conversions Plus (for Windows PC’s).

Once you understand file formats better, they are less frustrating and you have time to move on to other, more interesting problems. If they are computer problems please consider phoning Mac Rory at (360) 695-6929.

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