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Sep
24
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After introducing the Msi platform in Article 1, I would like now to take a deeper look at its “roll-back” feature.
The idea of having an Msi platform is to register all the actions during the installation process and enable their retrieval (“roll-back”). Each and every action is logged in two separate locations:
- c:\WINDOWS\Installer – stores a transformed copy of the original Msi, according to the actions performed during the installation process. This copy is later used, for example, to enable “Remove/Repair” and other maintenance sequences.
In addition, this file stores the PackageCode. Most Installation Editor Programs define this code as default behavior and use it to determine when to run “Update/Maintenance” Mode. (The code can be queried by either opening the Msi through the editor, or by right clicking it and then selecting the “Properties Summary” tab or the “Revision Number” field.
- Registry Key – stores the GUIDs, as well as information about the features and components installed by each product and the relationship between them, as follows:Upgrade Code: A unique GUID defining the “family” of the product. This code is registered, after the installation is successfully completed, under: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UpgradeCodes.
Product Code: A unique GUID defining the installed product. This code is registered under: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\[user identifier]\Products and as a sub-key under the UpgradeCode. The [user identifier] marks the unique GUID which is given to each user of the machine. The extra sub-key helps to distinguish between per-machine and per-user installed products.
Features: The name of each installed feature and its encrypted data are listed under: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\[user identifier]\Products\[Transformed Product Code]\Features.
They supply the relationship information between the installed components of each product.
Components: The identifier GUIDs for all the components of each installed product are listed as a sub-key under: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\[user identifier]\Components\[Transformed Product Code].
They supply the relationship information between the installed components of each product. Note that the GUID registered here is the transformed one.
Patches: The list of patches installed for each product, and their properties, are listed under: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\[user identifier]\Products\[Transformed Product Code]\Patches\[Transformed Patch Code]/
Some of the terms mentioned in this article, such as “Feature”, “Components” and “patches”, will be clarified throughout the next articles of this series.
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