Comparative Study of Per-Machine vs Per-User Installation

Several common scenarios can arise when the choice of “Per-User” versus “Per-Machine” is given to the user:

           1.    Major Upgrades can Fail

If you use the Upgrade code feature of Windows Installer to perform a major upgrade the detection of the existing software will fail if:
(a) the original software was installed with ALLUSERS=”” and the new software has ALLUSERS=1 in its Property table or passed on the command line or
(b) the original software was installed with ALLUSERS=1 and the new software has ALLUSERS=”” or ALLUSERS is not defined in the Property table or on the command line.

            2.    Uninstall Problems

If two different users on the system install the software with ALLUSERS=”” they will both have their own shortcuts and Add/Remove Programs entries made (which is fine and is by design). However, if some of the files are installed to a shared location (such as "Program Files" Folder) and one of the users uninstalls the software, the other user will not be able to use the software even though their shortcuts and Add/Remove Programs entries are still intact. In other words, the two installed instances of the software will not “know” about each other.

3.    Support Issues

Multiple instances of an install means there is duplicate copies of binaries on the machine, which wastes disk space. A “Per-Machine” install creates a single copy of common binaries for all users thus saving space.

Software is less secure because updating behavior has to be done for each user on the machine. In other words, the occasional user on the machine can make the machine vulnerable because they are not on the machine often enough to keep the software they use up-to-date.