| Filename extension | .chm |
|---|---|
| Internet media type | application/x-chm |
| Developed by | Microsoft |
| Initial release | 1997 |
| Extended to | .lit |
| Standard(s) | No |
| Microsoft Compiled HTML Help A component of Microsoft Windows |
|
|---|---|
| Details | |
| Type | Help system |
| Included with | Windows 98 |
| Replaces | Microsoft WinHelp |
| Replaced by | Microsoft Help 2 |
Microsoft Compiled HTML Help is a Microsoft proprietary online help format. It was introduced as the successor to Microsoft WinHelp with the release of Windows 98, and is still supported in Windows 7.
Contents |
In 2002, Microsoft announced security risks associated with the .CHM format, as well as security bulletins and patches.[1] They have since announced their intentions not to develop the .CHM format further.[2]
| 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. |
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 starts with bytes "ITSF" (in ASCII), for "Info-Tech Storage Format". The format has been reverse-engineered by Matthew Russotto with assistance from Peter Ferrie and Paul Wise.[3] Russotto's documentation is freely available at http://www.russotto.net/chm/chmformat.html.
On Windows computers a .chm can be built with the freely-distributed HTML Help Workshop.
The published help features:
The .chm file format's ability to contain and execute arbitrary code is a potential security threat, and viewing .chm files is sometimes restricted in the Windows OS.
The Microsoft Reader .LIT file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.[5]
Sumatra PDF supports viewing CHM documents since version 1.9.
Beyond CHM, a multi-tab CHM reader and CHM editor, which enables user to add annotations on CHM eBooks.
Various applications, such as HTML Help Workshop or 7-Zip, have features to decompile CHM files. On Windows systems, the hh.exe utility, as well as the extract_chmLib utility (a component of chmlib) on Linux systems, can be used to decompile CHM files as well.
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