File Types

Because files can have different purposes, they have different types. The file type is best identified by its file structure. For example a text file would have a very different structure than a file than can be executed. An executable file must have a specific structure to be able to be run. The file structure is used to determine its MIME type. The word MIME stands for multipurpose internet mail extension and is used as a standard to identify various file types.

File Extensions

In operating systems such as Microsoft Window systems, Linux, and Unix, a file extension is used to help identify the type of file. On Microsoft Windows systems, many file types are associated with a particular program which can read the file. For example a file with a .pdf extension can be read by the Adobe Acrobat application program.

Files are actually identified by what is called a MIME type. This can be done because files that are executable have a different structure than a data structure. Therefore file extensions are not the only way to identify a file type nor are they the most accurate. Apple MacIntosh computer systems do not use a file extension to identify file types.

Executable File Types

The most important file type to be aware of are executable file types. This is because if you accidentally run an executable file on your system, it may install a virus or some other unwanted software program. Executable file types include:

• .com
• .exe

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What Files Are

Files are a collection of data onto a permanent storage structure. They are stored on a permanent storage media such as a computer hard drive, CD ROM drive, floppy disk drive or sometimes even a tape drive. Files take a certain amount of room to store. For example if you have two text files and one file has one sentence in it while the other file has 200 sentences in it, the file with 200 sentences will use more room on the storage media.

File Functions

Different files have different purposes. Files are used to do one or more of the following functions:

• Provide machine executable code which is used to run application programs and the operating system.
• Store application program or operating system configuration information.
• Store data used by the user such as Microsoft Word document files.

Therefore there are three types of information that files contain:

• Executable code.
• System or program configuration information.
• User data.

These files are read by an application program or the operating system.

File Characteristics

Files have the below characteristics:

• Name
• Optional extension name - Part of the name, it is used by Windows operating systems to identify an associated program that can be used to read it
• Size - Shows the space the file requires for storage normally showed in kilobytes (Kb) which is 1000 bytes
• Type - Indicates the program used to access the file. The next section will talk more about file types.
• Date Modified - Shows the last date the file was created or changed.
• File structure - This characteristic is not viewable by the computer user but some programs can examine file structure to determine the type of file it is even when the file extension is changed.

The main items to remember include the facts that all files take a certain amount of room on their storage media and all files have a type which indicates whether they can be run by your computer. The file extension is one indication of the file type but not the only way to determine type.

If you are browsing your files using "My Computer" and click on "View" and "Details" you will see a window showing the file characteristics like the one below. Folders only take a little room on the hard drive and do not normally take as much room as files.

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