Microsoft Compiled HTML Help

Last updated
Microsoft Compiled HTML Help
Filename extension
.chm
Internet media type
application/vnd.ms-htmlhelp [1]
Developed by Microsoft
Initial release1997
Latest release
1.4 [2]
Extended to .lit
Microsoft HTML Help Executable
Other nameshh.exe
Developer(s) Microsoft
Included with Microsoft Windows
Predecessor Microsoft WinHelp
Successor Microsoft Help 2
Type Help system

Microsoft Compiled HTML Help (CHM) 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.

Contents

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 [3] [4] and is still supported in Windows 11. [5]

MonthYearDescription
February1996 Microsoft announces plans to stop development of WinHelp and start development on HTML Help.
August1997HTML Help 1.0 (HH 1.0) is released with Internet Explorer 4.
February1998HTML Help 1.1a ships with Windows 98.
January2000HTML Help 1.3 ships with Windows 2000.
JulyHTML Help 1.32 releases with Internet Explorer 5.5 and Windows Me.
October2001HTML Help 1.33 releases with Internet Explorer 6 and Windows XP.
MarchAt the WritersUA (formerly WinWriters) conference, Microsoft announces plans for a new help platform, Help 2, which is also HTML based.
January2003Microsoft 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. [6]

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. [7] [8]

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. [9]

CHM files support the following features:

The Microsoft Reader's .lit file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books. [11]

Viewers

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

NameOperating systemWebsite
Okular Windows, Linux, Unix-like 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

GnoCHMLinux, BSD GnoCHM on SourceForge
CHM ViewNone/Uncompiled chmviewkit on GitHub
kchmviewerWindows, Linux ulduzsoft.com/kchmviewer/
KCHMLinux, BSD, Solaris KCHM on SourceForge
CHMPaneWindows, macOS, Linux CHMPane on SourceForge
CHMate NeueiOS, iPadOS, visionOS CHMate Neue on iTunes
iChmiOS, macOS iChm on iTunes Discontinued
ChmPlusiOS, iPadOS, macOS, visionOS ChmPlus on iTunes
ChmoxmacOS chmox.sourceforge.net

Chmox on SourceForge

ClearviewmacOS Clearview on iTunes
DisplayCHMLinux linux-apps.com/p/998057
KOReaderAndroid, Linux koreader.rocks

Koreader on GitHub

Creators

Microsoft's HTML Help Workshop generates CHM files by instructions stored in a HTML Help project file, which bears a .HHP file name extension and is a specialized form of INI file. [12]

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

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. ↑ "Microsoft Security Bulletin MS02-055 - Critical". docs.microsoft.com. Retrieved 2020-10-29.
  4. ↑ "Full Disclosure: HtmlHelp - .CHM File Heap Overflow". seclists.org. Retrieved 2020-10-29.
  5. ↑ "[SOLVED] Windows 10 CHM Help Files showing up blank. - Spiceworks". community.spiceworks.com. Retrieved 2020-10-29.
  6. ↑ "Microsoft HTML Help Downloads". Microsoft. Retrieved 6 March 2012.
  7. ↑ Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification" . Retrieved 15 August 2012.
  8. ↑ Palade, Alexandru (2005). "Archive::Chm" . Retrieved 22 July 2014.
  9. ↑ "Virus Bulletin :: Chamber of horrors". www.virusbulletin.com. Retrieved 2022-01-05.
  10. ↑ "INFO: Limited Unicode Support in HTML Help". Microsoft. 11 April 2001. Archived from the original on 13 March 2016. Retrieved 17 March 2012.
  11. ↑ Salomon, David; Motta, Giovanni; Bryant, David (CON) (2009). Handbook of Data Compression (5th, illustrated ed.). Springer. ISBN   978-1-84882-902-2.
  12. ↑ Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification INI formats" . Retrieved 1 February 2018.
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