Windows 3.1

Compatibility has been a key aspect of Microsoft's Windows operating system since its early days. In Windows 3.1, users had to identify applications themselves, as seen with the ambiguity of C:MAILMAIL.EXE representing either Microsoft Mail or cc:Mail for MS-DOS. The APPS.INF file was a guide, but users bore the responsibility for compatibility. With the launch of Windows 95, an application compatibility database was introduced, allowing the OS to adapt using compatibility flags and enabling automatic patching of programs. The Windows 95 team sought written permission from vendors before patching third-party code, ensuring that future versions would not rely on temporary patches. Detection of applications eligible for patches became systematic in Windows 95, utilizing detection strings stored in the Registry. These strings were designed sequences decoded into bytes, with the initial byte determining the matching algorithm. File size matches were common, while file content matches were rare due to I/O costs. Naming conventions for patches included 'Add' and 'Change,' with numeric suffixes for multiple patches of the same type. Microsoft's commitment to backward compatibility has been a significant factor in its success, particularly during the late 20th and early 21st centuries.