Information Technology Reference
In-Depth Information
Every file and subdirectory has a directory entry. The root directory doesn't
have an entry.
File Entries
Table 9-1 shows the contents of a directory entry. The essential fields are the
DOS 8.3 fields. The additional fields are optional for many applications.
The File Name
The file-name field at byte zero contains the characters before the dot. The
file-extension field at byte 8 contains the characters after the dot. (The dot
isn't stored in the directory.) All text is upper case.
In an entry that contains a file name, any unused locations in the file-name
and extension fields should contain the code for a space (20h).
In an unused entry, the first byte in the file-name field is 00h or E5h. The
value 00h means that all of the entries that follow in the directory are also
available.
An 8.3 name has several limitations:
•
Each character code in the file name and extension is eight bits. Original
8.3 entries in PCs use character codes from the system's OEM code page,
which defines character codes for a geographical region.
•
All text characters are stored as upper case.
•
An 8.3 file name must begin with a letter or a number. In addition to
upper-case letters and numbers, a name can contain spaces and any of
these characters:
$ % ' - _ @ ~ ' ! ( )
•
Windows doesn't allow any of these as file names: CON, AUX, COM1-
COM4, LPT1-LPT3, PRN, NUL.
Attributes
The Attributes field at byte 11 contains six bits that provide information
about the entry. Table 9-2 lists the bits and their meanings. If bits 0-3 are all
1s, the entry is a long-file-name entry.
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