Monday, May 2, 2016

How does Windows figure out the size of an installed program?

In the Programs and Features dialog, you see that some entries have a value in their Size column. The obvious question is, how does Windows figure that size out?

The answer is that it doesn't, at least as of Windows 7. The value is set by the program's installer at install time. That value could conceivably be wildly off the mark from the actual space used by the program's files, but that's not a concern of Windows. Windows keeps the information in a value called EstimatedSize in the program's entry in the Uninstall key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall

Programs without that Registry entry simply have no value in the Size column.

Windows versions prior to 7, when confronted with a program that doesn't supply its own size estimation, would do some disk searching to guess.

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