Processes Maintain Only One Current Directory

Last reviewed: December 16, 1996
Article ID: Q84244

The information in this article applies to:

Microsoft Win32 Application Programming Interface (API) included with:
```
    - Microsoft Windows NT versions 3.1, 3.5, 3.51, and 4.0
```

SUMMARY

Processes under Windows NT maintain only one current directory. Under MS-DOS or OS/2, a process will maintain a current directory for each drive.

MORE INFORMATION

For example, if you do the following

Set the current drive to be drive C and set the current directory to be \MAINC\MAINSUBC.
Change the current drive to be drive D and set the current directory to be \MAIND\MAINSUBD.

When you reset the current drive to drive C, the current directory will be the original directory: \MAINC\MAINSUBC.

MS-DOS and OS/2 use a current directory structure (CDS) to maintain this information. The memory for this structure is allocated at boot time, and is set by the LASTDRIVE= line in the CONFIG.SYS file. For example, if you set LASTDRIVE=Z, you will have 26 entries in the CDS and will be able to track 26 current directories.

Windows NT by default allows a process to track only one current directory- -the one for the current drive--because the underlying operating system does not use drive letters; it always uses fully-qualified names such as:

   \Device\HardDisk0\Partition1\autoexec.bat

The Win32 subsystem maintains drive letters by setting up symbolic links such as:

   \??\C: == \Device\HardDisk0\Paritition1
   \??\D: == \Device\HardDisk0\Paritition2
   \??\E: == \Device\HardDisk1\Paritition1

(Partitions are 1-based while hard disks are 0-based because Partition0 refers to the entire physical device, which is the "file" that FDISK opens to do its work.) Therefore, when you do SetCurrentDirectory("c:\tmp\sub"), the Win32 subsystem translates that to "\??\c:\tmp\sub", "...".

As far as Windows NT is concerned, there are no "drives," there is one object name space.

CMD.EXE maintains a private current directory for each drive it has touched and uses environment variables to associate a current directory with each drive.

KBCategory: kbprg
KBSubcategory: BseFileio
Additional reference words: 3.1 3.5 3.51 4.0 Path Directory Current Drive

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Last reviewed: December 16, 1996
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