How Windows 95 fought off badly behaved installers

Microsoft veteran Raymond Chen has shared another nugget of Windows lore – what Windows 95 did when installers stomped on its system files. The problem traces back to the days of 16-bit Windows, when many system components were redistributable. Installers could include copies of those components and place them on a target computer. The setup program was expected to compare the version numbers of what was on the system and what was being copied, only overwriting if the file being installed had a higher version number. Simpler days compared to the pain of creating install sets now and worrying about wholesale registry destruction, or a dependency not being what a developer thought it was. "This rule relies on the fact that Windows maintains backward compatibility, so the newer version still works even if used by an older program," Chen wrote. In practice, nothing stopped an installer from ignoring that rule entirely. It was not uncommon for setup programs to simply overwrite whatever was in their way, replacing Windows 95 components with their Windows 3.1 counterparts. "You can imagine how much of a disaster this caused to the rest of the system," said Chen. At this point, even though it is many decades since the era of Windows 95, a reader would be forgiven for wondering why the operating system allowed this at all. The answer is backward compatibility: blocking file operations risked breaking the installer itself. Once upon a time, saving your bits meant punching holes in floppies How Microsoft's legal eagles wrangled Happy Days for Windows 95 Microsoft veteran explains the one weird trick that made Windows 95 restart faster How Microsoft gave customers what they wanted: An audience with Bill Gates "This ended up creating more problems," explained Chen. "Some installers declared the installation to be a failure and gave up. [Others] displayed an error message to the user and asked the user what to do next. (Like the user knows what to do next.)" "You even had installers that took even more extreme measures and said, 'Okay, fine, I can't overwrite the file, so I'm going to reboot the system and then overwrite the file from a batch file, see if you can stop me.'" Microsoft's solution was a hidden directory (c:\windows\sysbckup ) of commonly overwritten files. After setup finished, Windows quietly checked the file version numbers on the disk. Higher version numbers would be copied into the hidden directory, or the file in the hidden directory would replace a lower version number. "Basically," wrote Chen, "Windows 95 waited for each installer to finish, and then went back and checked its work, fixing any mistakes that the installer made." The belt-and-braces approach depended on the operating system being aware of a setup program rummaging through its internals. Today - based on recent performance - users should worry less about installers and more about what Microsoft itself is doing to Windows' system files. ® × Narrower topics Active Directory Android Azure Bing Bitlocker BSoD CentOS Debian Elementary OS Excel Exchange Server Firmware HoloLens Internet Explorer iOS LinkedIn Linux macOS Microsoft 365 Microsoft Build Microsoft Edge Microsoft Fabric Microsoft Ignite Microsoft Office Microsoft Surface Microsoft Teams .NET Office 365 OS/2 Outlook Patch Tuesday Pluton PowerShell Qubes SharePoint Skype SQL Server Ubuntu UEFI Unix Visual Studio Visual Studio Code Windows 10 Windows 11 Windows 2000 Windows 7 Windows 8 Windows Server Windows Server 2003 Windows Server 2008 Windows Server 2012 Windows Server 2013 Windows Server 2016 Windows Subsystem for Linux Windows XP WPF Xbox Xbox 360