Over the past few years, interesting facts about the history of Microsoft Windows have been exposed: from why the graphical interface strategy has been fragmented for a long time, to the many "interesting gadgets" hidden in the Windows 95 installation CD, to those unpopular tricks that help older computers restart faster. Recently, another veteran Microsoft employee shared a little-known story about how Windows 95 dealt with "troublesome" installers.
According to Raymond Chen, an engineer who was responsible for Windows at Microsoft, in the Windows 95 era, many third-party software installers would come with a batch of system redistributable components to ensure that the software could run smoothly on the user's computer. The official guidance given by Microsoft at the time was: When copying these components, the installer must first detect whether the component with the same name already exists in the system and whether the existing version is updated; only if the component does not exist in the system, or the system version is older, it can be overwritten and installed.
However, in reality not all developers adhere to this norm. Some installers ignore version checks and simply replace system components with their own bundled files, regardless of whether the system has a new version or an old version. As a result, key components of Windows 95 that had been updated to newer versions were instead rolled back to older versions, causing other software that relied on newer version components to experience various abnormalities or even crash, and the system stability was also greatly reduced.
Faced with this risk of being "regressed", Microsoft finally designed a compromise that was not fancy but very practical: maintain a hidden backup directory named C:WindowsSYSBCKUP in the system directory. This directory holds copies of critical system components that are most commonly overwritten by external installers. When the installation program finishes running, Windows 95 will quietly perform a "version comparison" in the background: comparing the current "new" components of the system with the backup versions in the SYSBCKUP directory one by one.
If it is found that a component has been replaced by an older version by the installer, the system will replace it with a newer copy saved in SYSBCKUP without the user being aware of it, which is equivalent to automatically "undoing" the erroneous overwrite. If it is detected that the installation program does bring a higher version of the component, Windows 95 will synchronously update the corresponding backup file in SYSBCKUP so that it can continue to be used as a recovery baseline in the future.
Chen said that from an engineering perspective, this approach is actually relatively "raw", but it is far better than some of the crude solutions Microsoft initially tried. For example, Microsoft initially tried to directly prevent the installer from overwriting system component files. This can indeed protect the system, but the cost is that a large number of installation processes will fail because of this, and users can only face error prompts but have no way to solve it. Another idea is to have the installation program write a "dummy file". On the surface, it looks like the overwriting is successful, but in fact, the real components are not touched. But this solution also doesn't work, because many installation programs will also verify the writing results. If the file content or verification value is found to be inconsistent, an error will pop up to terminate the process.
After these solutions exposed obvious flaws, the "post-facto correction" mechanism using the SYSBCKUP directory became the best balance between reliability and flexibility at that time: it not only allowed the third-party installation program to complete normally, but also automatically repaired the potential damage it caused to key system components in the background, greatly reducing the probability that ordinary users would "break Windows just by pretending to install it" when installing software on a daily basis.