What is the ISM file format?
An .ism file is an InstallShield project file - the editable source representation of a Windows installer package, maintained by Revenera (formerly Flexera Software) as part of the InstallShield product line.
The name "ISM" deliberately reverses "MSI": the .ism source is compiled by InstallShield into a distributable .msi Windows Installer package for end-user deployment.
Two storage modes exist. In XML mode (strongly recommended), the .ism is a UTF-8 text file rooted at an <ISWiProject> element whose structure mirrors the Windows Installer database schema - tables for components, features, files, registry entries, custom actions, dialogs, and launch conditions. In binary mode the same data is stored as an OLE2 Compound Document with magic bytes D0 CF 11 E0 (identical to .msi, .xls, and .doc files). XML mode is essential for version control with Git or SVN; binary mode produces identical build output but is not diff-able.
A SchemaVersion attribute in the root element records the InstallShield version that created the project. Older InstallShield versions cannot open a project whose SchemaVersion exceeds their own.
Beyond the base Windows Installer schema, .ism projects support InstallShield-specific features: setup prerequisites, suite installers, QuickPatch projects, and merge module references (.msm files). As of 2024, InstallShield is marketed under the Revenera brand within Flexera's software monetization portfolio.
Security & safety
RISK: MEDIUMAn .ism file in XML mode is a passive text file. In binary (OLE2) mode it is an MSI database - which can contain custom actions (DLL calls, EXE execution, VBScript/JScript). Binary .ism files from unknown sources carry the same risk as .msi files: custom actions execute during any build or inspection that triggers MSI processing. Review custom action entries before processing .ism files from untrusted sources.
Format details
in a nutshell- IIS Smooth Streaming Manifest - Microsoft IIS Media Services uses .ism as the server manifest for Smooth Streaming adaptive bitrate video - an XML file pointing to audio/video tracks. Completely unrelated to InstallShield.
- Cakewalk Sonar instrument file - Some versions of Cakewalk/SONAR digital audio workstation used .ism for soft-synth instrument definitions.
Programs that open ISM files
Windows3 apps
InstallShield (by Revenera/Flexera)
Paid Open .ism via File > Open Project. Full IDE with drag-and-drop file/registry editors and build system. Compatible InstallShield version must match or exceed the project's SchemaVersion.
Notepad++ (XML view, read-only)
Open-source Open XML-mode .ism to inspect or diff content. Not suitable for editing - use InstallShield IDE.
Visual Studio Code (XML mode, read-only)
Open-source Open XML-mode .ism for text review and source control diffing. XML extension provides syntax highlighting. Technical details
deep spec| Storage modes | XML (UTF-8 text, recommended) or binary OLE2/MSI Compound Document |
| XML root element | <ISWiProject> |
| Binary mode magic bytes | D0 CF 11 E0 A1 B1 1A E1 (OLE2 Compound Document - same as .msi, .xls, .doc) |
| Compiled output | .ism project compiles to a .msi Windows Installer package for distribution |
| Schema versioning | SchemaVersion attribute in XML root records the creating InstallShield version |
| Version control | XML mode enables Git/SVN diff; binary mode output is identical but non-diff-able |
| Extended features | Setup prerequisites, suite installers, QuickPatch projects, merge modules (.msm) |
| Name etymology | "ISM" = "MSI" reversed - deliberate naming by InstallShield |
| Typical file size | 50 KB-5 MB (complex enterprise installers with many components) |
| OS scope | Windows only - builds Windows Installer packages targeting Windows deployments |
| Compatibility direction | Newer InstallShield opens older .ism; older versions cannot open higher SchemaVersion |
| Current brand | Revenera (product line within Flexera Software) |
| Released | ~1999 (InstallShield became a major product; ISM as primary project format introduced in InstallShield 7.x, ~2001) |
| Latest version | InstallShield 2024 R1 (Flexera/Revenera) |
| Specification | docs.revenera.com |
ISM conversions
Community Q&A
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