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GeezerVison is showing en.wikipedia.org — Microsoft Compiled HTML Help - Wikipedia

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Microsoft Compiled HTML Help
Filename extension
.chm
Internet media type
application/vnd.ms-htmlhelp[1]
Developed byMicrosoft
Initial release1997
Latest release
1.4[2]
Extended to.lit
Microsoft HTML Help Executable
Other nameshh.exe
DeveloperMicrosoft
Included withMicrosoft Windows
PredecessorMicrosoft WinHelp
SuccessorMicrosoft Help 2
TypeHelp system

Microsoft Compiled HTML Help (CHM)[a] is a Microsoft proprietary online help format, consisting of a collection of HTML pages, an index and other navigation tools. The files are compressed and deployed in a binary format with the extension .CHM. The format was intended to succeed Microsoft WinHelp.

Although the format was designed by Microsoft, it has been successfully reverse-engineered and is now supported by many document viewers.

History

CHM was introduced as the successor to Microsoft WinHelp with the release of Windows 95 OSR 2.5. Within the Windows NT family, the CHM file support is introduced in Windows NT 4.0[4][5] and is still supported in Windows 11.[6]

Month Year Description
February 1996 Microsoft announces plans to stop development of WinHelp and start development on HTML Help.
August 1997 HTML Help 1.0 (HH 1.0) is released with Internet Explorer 4.
February 1998 HTML Help 1.1a ships with Windows 98.
January 2000 HTML Help 1.3 ships with Windows 2000.
July HTML Help 1.32 releases with Internet Explorer 5.5 and Windows Me.
October 2001 HTML Help 1.33 releases with Internet Explorer 6 and Windows XP.
March At the WritersUA (formerly WinWriters) conference, Microsoft announces plans for a new help platform, Help 2, which is also HTML based.
January 2003 Microsoft decides not to release Microsoft Help 2 as a general Help platform.

Microsoft has announced that they do not intend to add any new features to HTML Help.[7]

File format

Help is delivered as a binary file with the .chm extension. It contains a set of HTML files, a hyperlinked table of contents, and an index file. The file format has been reverse-engineered and documentation of it is freely available.[8][9]

The file starts with bytes "ITSF" (in ASCII), for "Info-Tech Storage Format", which is the internal name given by Microsoft to the generic storage file format used for CHM files.[10]

CHM files support the following features:

  • Data compression (using LZX)
  • Built-in search engine
  • Ability to merge multiple .chm help files
  • Extended character support, although it does not fully support Unicode.[11]

The Microsoft Reader's .lit file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.[12]

Viewers

In addition to Microsoft Windows, the following apps support CHM:

Name Operating system Website
Okular Linux, Unix-like, Windows okular.kde.org

invent.kde.org/graphics/okular

 Uses hh.exe on Windows
Calibre Windows, macOS, Linux calibre-ebook.com

calibre on GitHub
Sumatra PDF Windows www.sumatrapdfreader.org

sumatrapdf on GitHub
GnoCHM Linux, BSD GnoCHM on SourceForge
CHM View None/Uncompiled chmviewkit on GitHub
kchmviewer Windows, Linux ulduzsoft.com/kchmviewer/
KCHM Linux, BSD, Solaris KCHM on SourceForge
CHMPane Windows, macOS, Linux CHMPane on SourceForge
CHMate Neue iOS, iPadOS, visionOS CHMate Neue on iTunes
iChm iOS, macOS iChm on iTunes Discontinued
ChmPlus iOS, iPadOS, macOS, visionOS ChmPlus on iTunes
Chmox macOS chmox.sourceforge.net

Chmox on SourceForge
Clearview macOS Clearview on iTunes
DisplayCHM Linux linux-apps.com/p/998057
KOReader Android, Linux koreader.rocks

Koreader on GitHub
7-zip Windows (GUI), MacOS (command-line), Linux (command-line) www.7-zip.org

Ip7z on GitHub

 7-zip can show the contents of .chm files as though they are a compressed archive, but does not render the HTML as a help-viewer.

Creators

Microsoft's HTML Help Workshop generates CHM files by instructions stored in an HTML Help project file, which bears a .HHP file name extension and is a specialized form of INI file.[13]

Lazarus and Free Pascal provide a doxygen-like tool for CHM generation and a separate command-line compiler called chmcmd.

Other utilities

The official viewer in Microsoft Windows (hh.exe) can decompile a CHM file. So can Microsoft HTML Help Workshop and 7-Zip. Calibre and arCHMage can convert CHM into another format.

See also

Wikibooks logo
The Wikibook Windows Programming has a page on the topic of: Compiled HTML Help
  • WinHelp
  • Microsoft Help 2
  • Comparison of documentation generators

Footnotes

  1. ↑ An initialism of "Compiled Help Module".[3]

References

  1. ↑ Techtonik, Anatoly (11 April 2006). "application/vnd.ms-htmlhelp". Retrieved 7 March 2012.
  2. ↑ "Microsoft HTML Help 1.4". Windows Dev Center. Microsoft. Retrieved 10 January 2017.
  3. ↑ "System Requirements". Microsoft Sync Framework Documentation. Microsoft Download Center. 2024-07-15. Note: On computers with security update 896358 installed, downloaded Compiled Help Module (CHM) files cannot be opened by default.
  4. ↑ "Microsoft Security Bulletin MS02-055 - Critical". docs.microsoft.com. Retrieved 2020-10-29.
  5. ↑ "Full Disclosure: HtmlHelp - .CHM File Heap Overflow". seclists.org. Retrieved 2020-10-29.
  6. ↑ "[SOLVED] Windows 10 CHM Help Files showing up blank. - Spiceworks". community.spiceworks.com. February 2017. Retrieved 2020-10-29.
  7. ↑ "Microsoft HTML Help Downloads". Microsoft. Retrieved 6 March 2012.
  8. ↑ Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification". Retrieved 15 August 2012.
  9. ↑ Palade, Alexandru (2005). "Archive::Chm". MetaCPAN. Retrieved 22 July 2014.
  10. ↑ "Virus Bulletin :: Chamber of horrors". www.virusbulletin.com. Retrieved 2022-01-05.
  11. ↑ "INFO: Limited Unicode Support in HTML Help". Microsoft. 11 April 2001. Archived from the original on 13 March 2016. Retrieved 17 March 2012.
  12. ↑ Salomon, David; Motta, Giovanni; Bryant, David (CON) (2009). Handbook of Data Compression (5th, illustrated ed.). Springer. ISBN 978-1-84882-902-2.
  13. ↑ Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification INI formats". Retrieved 1 February 2018.

External links

  • HTML Help Web Page on MSDN Archived 2008-04-12 at the Wayback Machine
  • Microsoft Help 2 Reference Archived 2008-04-18 at the Wayback Machine (part of Visual Studio SDK for VS7.1 and VS8.0)
  • History of HTML Help
  • Unofficial (Preliminary) HTML Help Specification (the linked ITSF specification has been moved to the Russotto.net domain)
Retrieved from "https://en.wikipedia.org/w/index.php?title=Microsoft_Compiled_HTML_Help&oldid=1383703982"
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