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Using your personal computer |
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Hilton Head Island Computer Club |
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File Types |
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Now, with the updates to Windows, Outlook, Outlook Express, Internet Explorer, etc. to reduce security problems, certain types of files are blocked from downloading or running. The problem as I see it is that Microsoft default settings for all versions of Windows do not show file types. In an article I wrote for the February newsletter called File Management, I described how to use Windows Explorer/My Computer to see file types. You can also get to that article from my home page: http://users.hargray.com/ffahey/FFhome.htm. In this article I would like to talk some about the reasons for file types and some of the rules on their use. To begin with we need an operating system (OS) to manage and control how a computer runs and how it accepts and controls files to perform its function. From the days of DOS to all the Windows OSs, a large number of file types are used by the OS and for inter-facing with the various devices and programs that run on the OS. Next, each program that runs on the OS creates and manages more file types for the program to do and create its purpose and job. File names are created by the combination of a description and a type portion and separated by a period/dot. In the days of DOS, the format was 8 alphanumerical characters for the description and 3 alphanumerical for the file type. Because some additional characters can be used, there could be more than 50,000 types. When Windows 95 was introduced, they expanded the rules on file names. You could use up to 254 characters including spaces and periods in the description side and up to 4 in the type portion. There is a problem with allowing so many characters for the description portion because about the same amount of characters for the entire path and file name is required. When you need to locate a file, you need the name and where it is located, thus the total path/file length. You should try to write a file name so that you can understand what you were creating, but not so long that it creates a problem. Many programs will fill a name in for you (including Microsoft programs), which are quite long and then with path will not be accepted by the OS. Once you know the file type, you can determine if it is a generic or one assigned to a particular program. Generic type formats are normally those that have been created by some standards organization or by an industry group. A listing at http://www.computeruser.com/resources/dictionary/filetypes.html will show many but not all types used. For example, not listed is PQI, which is the image file for Drive Image from Power Quest. Another reason, and maybe the most important, is how they affect our use of the files. In the earliest days of DOS you opened a program and then opened or created a particular file associated with that program. You got to name the file and only sometimes did they add the extension (3 alphanumerical characters). Early versions of WordPerfect did not require any extension. Macintosh always used and associated with file extensions. And, when Microsoft began to use Windows OSs, they also started associations with programs and file types. It would show up in a compatibility section of win.ini. When you opened, ran or double clicked on a file listed in the compatibility section, the associated program would open and then the file that you had selected. As we moved into Windows 95, Microsoft combined all the information from DOS and prior Windows OSs into the Registry. The registry has five keys and the first is HKEY_CLASSES_ROOT which has all the information on all installed programs and which one will respond to a particular extension. The association with file types can be found in the Folder Options, which is found in Windows Explorer/My Computer under either View or Tools depending on your OS. Also, it is often in the Control Panel. When you open Folder Options, you will find the Files Type tab and clicking on it will show all the types associated with programs on your computer. If you attempt to open any file type that is not listed there, you get a dialog box that asks which program you want to use to open the file. In general it is best is to shut the box before you create a problem. That box usually has a check mark selected that says always use this program to open this type of file. Now, if you were someone who could not see extensions, you do not even know what you are dealing with and could create a registry entry that could limit opening that type in the future, even if you had the proper program installed. If you are curious, you could uncheck the box above and select Notepad to open it. If it is an ASCII type file (limited to letters and numbers and some control character) you may be able to read something about the file. If it comes up with funny symbols, forget about it. |
