Veteran Microsoft engineer Raymond Chen has confirmed what we all suspected about Windows 95: it guessed when a setup program was running.

Rather than relying on any special flag or marker, Chen explained that Windows 95 looked at the program's name to determine whether it was a setup application. It did this by checking the app against a list of magic words. If the program name contained one of them, it must be a setup. Chen gave the list: setup, install, inst, imposta, ayarla, and felrak.

While modern developers might look in horror at the sheer randomness of the concept – after all, these days it is easy to detect when a package is being disgorged in Windows – things were different in the 1990s, and Microsoft's operating system engineers had to make do with what they had.

"The entry for install is redundant with inst," wrote Chen, "because anything that contains 'install' will also contain 'inst'. My guess is that 'install' came first, and then later somebody found that a lot of setup programs were called 'blahinst' for various values of 'blah' so they added an entry for 'inst', but failed to remove the redundant entry for 'install'."

If no match was found, the OS also checked the path to the executable for the word "setup." If the conditions were met, Windows 95 could then run its cleanup checks for improperly modified system files.

"As a special bonus," added Chen, "Windows 95 does a live file check after any multimedia driver installs via an INF file. I guess the multimedia team discovered that a lot of drivers overwrite system DLLs in their INF files, so they asked for a cleanup pass afterward."

It's easy to give modern Windows a hard time for its many irritations, but spare a thought for the Windows 95 engineers, forced to guess whether an app was an installer before sweeping up whatever mess it left behind. ®