Microsoft Compiled HTML Help

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 Compiled HTML Help
Developer(s)Microsoft
Operating systemMicrosoft Windows
PredecessorMicrosoft WinHelp
SuccessorMicrosoft Help 2
TypeHelp system

Microsoft Compiled HTML Help 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, for Compiled HTML. The format is often used for software documentation.

It was introduced as the successor to Microsoft WinHelp with the release of Windows 95 OSR 2.5[3] and consequently, Windows 98. Within the Windows NT family, the CHM file support is introduced in Windows NT 4.0[4][5][6] and is still supported in Windows 11.[7] Although the format was designed by Microsoft, it has been successfully reverse-engineered and is now supported in many document viewer applications.

  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. ^ ^ since IE 4 is bundled with OSR 2.5, hence adding the CHM file support for the first time^
  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. ^ ^ The information available is scarce, but any VM installation of WinNT 4.0 appears to give .CHM file support out of the box. It seems like it wasn't introduced in in Windows NT 3.51 due to NT 3.51 being intentionally limited to Internet Explorer 16-bit versions^
  7. ^ "[SOLVED] Windows 10 CHM Help Files showing up blank. - Spiceworks". community.spiceworks.com. Retrieved 2020-10-29.