MSI File Format

MSI file is an installer package file used in Microsoft Windows. More specifically, it is an archive, containing necessary data for installation and removing programs. You can recognize MSI format by extension ID .msi at the end of the filename.

About MSI File Format

The name of MSI extension originally stands for «Microsoft Installer», an earlier version of Windows Installer. MSI package describes an installation of a concrete program. Structure of the package is divided into two parts: components and features. The components are files, containing different registers, names of installing files and information, hidden from users. Despite that, features can be seen by the users. When we look at the selection dialog box, we choose options from the features list. MSI file contains a relational database with all information, and this file has the possibility to put user script and supporting libraries into it.

The installation process from MSI files has three steps. The first step is actions, standard operations of installing, which can be supplemented by user commands, written in the programming language. The second step is collection of information. Windows Installer collects instructions for the purpose of installing or deleting features. The third step is performing all commands. In the beginning of the process it is launched in privileged mode to avoid interruption of users without necessary rights. The fourth step is an exception, when the user wants to cancel the installation process, or there are some critical problems.

MSI Editors

As it was mentioned before, MSI file represents itself as an archive, and a common user can easily unpack it by using archivers like 7Zip or WinRAR. But any changes in the file are unavailable without special software due to the risk of damaging MSI package, which leads to inability of program installation.

For skilled and experienced users there are different MSI editors, providing the possibility to edit files. They can be easily found on the Internet, but most of these programs are unverified and unsafe. If you have the necessary skill, you can try Orca MSI editor. It is a tool for changing and creating databases, contained in MSI files. This instrument also provides a graphic interface for comfortable usability. Orca MSI can be downloaded only with Microsoft Development Kit components, which can be found on the official Microsoft website.

Another utility for editing MSI packages is MSI wrapper, developed by Exemsi. Sometimes it is required to convert an MSI file into an EXE file, and this tool has the most comfortable and understandable functionality for this purpose. It has an intuitive user-friendly interface, which can be mastered even by novice users.

You can download MSI wrapper from Exemsi webpage. It is distributed in two versions: free and pro, providing all features for commercial use.

Summary about MSI Files

MSI files and MSI packages are an essential part of the installation process in Microsoft Windows. You can influence it by changing features or using special tools, but in the second case you should be accurate to avoid file damage.