File Names in Windows XP Professional

File names in Windows XP Professional can be up to 255 characters and can contain spaces, multiple periods, and special characters that are not allowed in MS-DOS file names. Windows XP Professional makes it possible for other operating systems to access files that have long names by generating an MS DOS-readable (8.3) name for each file. These MS DOS-readable names also enable MS DOS based and Windows 3.x based applications to recognize and load files that have long file names. When a program saves a file on a computer running Windows XP Professional, both the 8.3 file name and long file name are retained.

Note 

The 8.3 format means that files can have between 1 and 8 characters in the file name. The name must start with a letter or a number and can contain any characters except the following:

. / \ [ ] : ; | = , * ? (space)

An 8.3 file name typically has a file name extension that is from one to three characters long and has the same character restrictions. A period separates the file name from the file name extension.

Several special file names are reserved by the system and cannot be used for files or folders:

CON, AUX, COM1, COM2, COM3, COM4, LPT1, LPT2, LPT3, PRN, NUL

To see both the long and short file names for each file in the folder, at the command line, type:

dir /x 

Long File Names at the Command Prompt

At the command prompt, if you type the long name of a file or folder that contains spaces, you must enclose the name in quotation marks. For example, if you have a program called Dump Disk Files that you want to run from the command prompt and you enter the name without quotation marks, it generates the error message Cannot find the program Dump or one of its components.

You must also use quotation marks around each referenced set of long file names when a path typed at the command line includes spaces, as in the following example:

move "c:\This month s reports\*.*" "c:\Last month s reports" 

Caution 

Use wildcard characters such as the asterisk (*) and question mark (?) carefully in conjunction with the del and copy commands. Windows XP Professional searches both long and short file names for matches to the wildcard character combination you specify, which can cause additional files to be deleted or copied. It is always a good idea to run the dir command first on the specified files to make sure you are affecting only the files you intend to use.

Generating Short File Names

In Windows XP Professional, both FAT and NTFS use the Unicode character set, which contains several prohibited characters that MS-DOS cannot read, for their names. To generate a short MS DOS-readable file name, Windows XP Professional deletes all of these characters from the long file name and removes any spaces. Because an MS-DOS-readable file name can have only one period, Windows XP Professional also removes extra periods from the file name. If necessary, Windows XP Professional truncates the file name to six characters and appends a tilde (~) and a number. For example, each non-duplicate file name is appended with ~1. Duplicate file names end with ~2, then ~3, and so on. After the file names are truncated, the file name extensions are truncated to three or fewer characters. Finally, when displaying file names at the command line, Windows XP Professional translates all characters in the file name and extension to uppercase.

Note 

You can permit extended characters by using the fsutil behavior set command. You must restart the computer before this setting takes effect. For more information about using the fsutil behavior set command, see Windows XP Professional Help.

When five or more files exist that can result in duplicate short file names, Windows XP Professional uses a slightly different method for creating short file names. For the fifth and subsequent files, Windows XP Professional:

• Uses only the first two letters of the long file name.

• Generates the next four letters of the short file name by mathematically manipulating the remaining letters of the long file name.

• Appends ~1 (or another number, if necessary, to avoid a duplicate file name) to the result.

This method substantially improves performance when Windows XP Professional must create short file names for a large number of files with similar long file names. Windows XP Professional uses this method to create short names for files on both FAT and NTFS volumes.

Table 13-15 shows the short file names for files created by six tests.

Table 13-15: Short File Names Created by Windows XP Professional Example One

Long File Name	Short File Name
This is test 1.txt	THISIS~1.TXT
This is test 2.txt	THISIS~2.TXT
This is test 3.txt	THISIS~3.TXT
This is test 4.txt	THISIS~4.TXT
This is test 5.txt	THA1CA~1.TXT
This is test 6.txt	THA1CE~1.TXT

If the long file names in Table 13-5 are created in a different order, their short file names are different, as shown in Table 13-16.

Table 13-16: Short File Names Created by Windows XP Professional Example Two

Long File Name	Short File Name
This is test 2.txt	THISIS~1.TXT
This is test 3.txt	THISIS~2.TXT
This is test 1.txt	THISIS~3.TXT
This is test 4.txt	THISIS~4.TXT
This is test 5.txt	THA1CA~1.TXT
This is test 6.txt	THA1CE~1.TXT

When you delete a file, its short file name is also deleted. When you create new files in the same folder, Windows XP Professional might re-use short file names that have been deleted. For instance, in Example 1, if you delete the file This is test 1.txt, and then create a new file called This is test 7.txt, its short file name becomes THISIS~1.TXT.