The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

Knowledge Base

Performance Degradation when Accessing Large Subdirectories

Article ID: 39535

Article Last Modified on 5/10/2003

APPLIES TO

Microsoft MS-DOS 2.11 Standard Edition
Microsoft MS-DOS 3.1
Microsoft MS-DOS 3.2 Standard Edition
Microsoft MS-DOS 3.21 Standard Edition
Microsoft MS-DOS 3.3 Standard Edition
Microsoft MS-DOS 3.3a
Microsoft MS-DOS 4.0 Standard Edition
Microsoft MS-DOS 4.01 Standard Edition
Microsoft MS-DOS 5.0 Standard Edition
Microsoft MS-DOS 5.0a
Microsoft MS-DOS 6.0 Standard Edition
Microsoft MS-DOS 6.2 Standard Edition
Microsoft MS-DOS 6.21 Standard Edition
Microsoft MS-DOS 6.22 Standard Edition

This article was previously published under Q39535

SUMMARY

You may notice a performance slowdown for MS-DOS when creating many files in a subdirectory. MS-DOS is much slower at accessing a subdirectory that contains many files or deleted files than at accessing a new subdirectory (that is, a subdirectory containing no deleted files).

This slowdown occurs because MS-DOS directories do not get smaller when you delete a file. MS-DOS inserts a "no file here" mark for each deleted file in a directory. There are two different "No file here" marks in the first bytes of directories:

   Value   Description
   -----------------------------------------------------------------
   E5H     No file at this location
   05H     No file at this location
   00H     No file at this location and no files after this location

Whenever you create a file, MS-DOS searches to the end of the directory to see if a file with that name already exists. Even if files have been deleted from the directory, MS-DOS must still check for the "No file here" entry for each deleted file.

MORE INFORMATION

The following is an example that demonstrates the reason for the performance slowdown:

Create a directory DIR. Initially, this new directory looks like the following:
```
      .
      ..
      00H
```
Create the file FILE1. MS-DOS has to look at two entries to determine that there is no file by that name. The directory now looks like the following:
```
      .
      ..
      FILE1
      00H
```
Create the file FILE2. MS-DOS now has to look at three entries to determine that there is no file by that name. The directory now looks like the following:
```
      .
      ..
      FILE1
      FILE2
      00H
```
Create the file FILE3. MS-DOS now has to look at four entries to determine that there is no file by that name. The directory now looks like the following:
```
      .
      ..
      FILE1
      FILE2
      FILE3
      00H
```

Delete FILE*. The directory now looks like the following:

Create the file FILE1. MS-DOS still has to look at four entries to determine that there is no file by that name. (Note that MS-DOS must look at the empty entries thus performance does not improve after the deletion.) The directory now looks like the following:
```
      .
      ..
      FILE1
      E5H
      E5H
      00H
```
Create the file FILE2. Again, MS-DOS has to look at four entries to determine that there is no file by that name. The directory now looks like the following:
```
      .
      ..
      FILE1
      FILE2
      E5H
      00H
```
Create the file FILE3. MS-DOS has to look at four entries to determine that there is no file by that name. The directory now looks like the following:
```
      .
      ..
      FILE1
      FILE2
      FILE3
      00H
```

The performance decreases more when deleted entries exist in a subdirectory; performance can be even slower, depending on the size and type of the disk and the size of the MS-DOS buffer cache (the BUFFERS command in the file CONFIG.SYS). Disk access is very expensive in terms of performance, and depending on the interaction with the MS-DOS buffer cache LRU (Least Recently Used) management, you may have to do more disk accesses.

There are third-party utilities that edit directories and eliminate unused directory entries, improving the performance of MS-DOS.

Additional query words: 6.22 2.x 3.x 4.00 4.01 5.00 5.00a 6.00 6.20 grows

Keywords: KB39535

Microsoft KB Archive/39535

Performance Degradation when Accessing Large Subdirectories

SUMMARY

MORE INFORMATION