MS-DOS installation compression

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A pair of compression formats by Microsoft that appear on MS-DOS and early Windows (3.x) installation disks; the formats have no generally agreed-upon name. Compressed files may be generated by the COMPRESS.EXE program (appearing in Microsoft's Setup Toolkit for Visual C++), and uncompressed with the EXPAND.EXE program distributed with Windows and MS-DOS. Compressed files have the last character of the file extension replaced with an underscore, or sometimes a dollar sign.
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'''MS-DOS installation compression''' refers to a family of compressed file formats formats by Microsoft that appear on MS-DOS and early Windows (3.x) installation disks. The formats have no generally agreed-upon name. This article is primarily about the format whose files start with "SZDD". For the other formats, see [[Microsoft KWAJ installation compression]] and [[Microsoft SZ installation compression]].
  
There are reports of the Google Chrome installer [http://festiva-yourchoice.blogspot.com/2010/01/expandexe-preventing-google-chrome-from.html needing the EXPAND.EXE program].
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Compressed files may be generated by the COMPRESS.EXE program (appearing in Microsoft's Setup Toolkit for Visual C++), and decompressed with the EXPAND.EXE program distributed with Windows and MS-DOS. Compressed files have the last character of the file extension replaced with an underscore, or sometimes a dollar sign.
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<!-- There are reports of the Google Chrome installer [http://festiva-yourchoice.blogspot.com/2010/01/expandexe-preventing-google-chrome-from.html needing the EXPAND.EXE program]. -->
  
 
== See also ==
 
== See also ==
This is not the only compressed file format for which the last character of the file extension might be replaced with an underscore. Others include:
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Other formats in this family:
* [[InstallShield installer archive]] (<code>_INST32I.EX_</code>)
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* [[Microsoft KWAJ installation compression]]
* [[FTCOMP]]
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* [[Microsoft SZ installation compression]]
* [[SQUEEZE (AJP Systems)]]
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* [[CAZIP]]
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Other formats that might be in this family:
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* [[FXPF]]
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* [[MRNZ]]
  
 
== Format details ==
 
== Format details ==
There are two major formats, which can be referred to by their file signatures: "SZDD", and "KWAJ". SZDD is more common. There is also a QBasic variant of SZDD format.
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SZDD's compression format is similar, but not identical, to [[LZSS (Haruhiko Okumura)|Okumura's LZSS]]. There is a byte at offset 8 that specifies the exact type of compression. Most sources say that the only known value for this byte is "A" (0x41), but some report[https://www.betaarchive.com/forum/viewtopic.php?t=26161] that there is also a type "B", used by Windows 3.1 builds 026 and 034e.
 
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=== SZDD ===
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SZDD format uses a simple form of [[LZSS]] compression. There is a byte at offset 8 that specifies the exact type of compression. Most sources say that the only known value for this byte is "A" (0x41), but some report[https://www.betaarchive.com/forum/viewtopic.php?t=26161] that there is also a type "B", used by Windows 3.1 builds 026 and 034e.
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=== KWAJ ===
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KWAJ format is somewhat more sophisticated than SZDD. There is a 16-bit field at offset 8 that specifies the compression or encoding method.
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{| class="wikitable"
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!Compression code !! Description
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|-
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|0 || Uncompressed
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|-
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|1 || [[Exclusive Or|XOR]]
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|-
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|2 || [[LZSS]]
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|-
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|3 || [[LZ77 with Huffman coding|LZ77 + Huffman]]
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|-
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|4 || [[MSZIP]] (based on [[DEFLATE]])
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|}
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== Identification ==
 
== Identification ==
File begin with bytes {{magic|53 5A 44 44 88 F0 27 33}} ("SZDD" variant), or {{magic|4B 57 41 4A 88 F0 27 D1}} ("KWAJ" variant), or {{magic|53 5A 20 88 F0 27 33 D1}} (QBasic SZDD variant).
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An SZDD file begins with bytes {{magic|53 5A 44 44 88 F0 27 33}}.
  
 
== Software ==
 
== Software ==
* [http://www.cabextract.org.uk/libmspack/ libmspack] → msexpand
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* [https://www.cabextract.org.uk/libmspack/ libmspack] → msexpand (decompress only)
 
* EXPAND.EXE - utility included with many versions of MS Windows and MS-DOS
 
* EXPAND.EXE - utility included with many versions of MS Windows and MS-DOS
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** [https://archive.org/details/1996-01-13-windows3.1windowsforworkgroups3.11intl Windows for Workgroups 3.11...] → WFW311/ENG_ARA/EXPAND.EXE - File Expansion Utility v2.10 (for DOS). This version of EXPAND.EXE supports SZDD, as well as KWAJ compression types 2 and 3.
 
* [ftp://ftp.microsoft.com/softlib/mslfiles/CP0982.EXE Setup Toolkit for Visual C++]
 
* [ftp://ftp.microsoft.com/softlib/mslfiles/CP0982.EXE Setup Toolkit for Visual C++]
 
* [[7-Zip]]
 
* [[7-Zip]]
* [ftp://ftp.penguin.cz/pub/users/mhi/mscompress/ mscompress] → msexpand
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* [https://github.com/stapelberg/mscompress mscompress] ([ftp://ftp.penguin.cz/pub/users/mhi/mscompress/ original version]) mscompress, msexpand (compression and decompression)
 
* [https://www.winehq.org/ Wine]
 
* [https://www.winehq.org/ Wine]
 
* {{Deark}}
 
* {{Deark}}
  
 
== Sample files ==
 
== Sample files ==
* https://telparia.com/fileFormatSamples/archive/msCompress/
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* {{DexvertSamples|archive/msCompress}}
  
 
== Links ==
 
== Links ==
* [http://support.microsoft.com/kb/80751 Documentation in Microsoft site]
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* [https://web.archive.org/web/20160527025701/https://support.microsoft.com/en-us/kb/80751 Documentation in Microsoft site] (archived)
* [http://www.cabextract.org.uk/libmspack/doc/szdd_kwaj_format.html SZDD and KWAJ formats description]
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* [https://www.cabextract.org.uk/libmspack/doc/szdd_kwaj_format.html SZDD and KWAJ formats description]
  
 
[[Category:File formats with too many extensions]]
 
[[Category:File formats with too many extensions]]

Latest revision as of 14:58, 28 April 2024

File Format
Name MS-DOS installation compression
Ontology
Extension(s) .??_, .??$
PRONOM fmt/462

MS-DOS installation compression refers to a family of compressed file formats formats by Microsoft that appear on MS-DOS and early Windows (3.x) installation disks. The formats have no generally agreed-upon name. This article is primarily about the format whose files start with "SZDD". For the other formats, see Microsoft KWAJ installation compression and Microsoft SZ installation compression.

Compressed files may be generated by the COMPRESS.EXE program (appearing in Microsoft's Setup Toolkit for Visual C++), and decompressed with the EXPAND.EXE program distributed with Windows and MS-DOS. Compressed files have the last character of the file extension replaced with an underscore, or sometimes a dollar sign.

Contents

[edit] See also

Other formats in this family:

Other formats that might be in this family:

[edit] Format details

SZDD's compression format is similar, but not identical, to Okumura's LZSS. There is a byte at offset 8 that specifies the exact type of compression. Most sources say that the only known value for this byte is "A" (0x41), but some report[1] that there is also a type "B", used by Windows 3.1 builds 026 and 034e.

[edit] Identification

An SZDD file begins with bytes 53 5A 44 44 88 F0 27 33.

[edit] Software

[edit] Sample files

[edit] Links

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