Some of the old software before 2010 may not be able to install/run normally on x64 or Windows 10 systems. Be aware of it before purchasing it.

Microsoft SQL Server 4.2 was shipped around 1992 (available bundled with IBM OS/2 version 1.3).
Microsoft SQL Server 4.21 was released in the Year 1993 by Microsoft for Windows NT and coincided with the release of Windows NT 3.1.