[snuxoll]

They did more than abstract their own system calls, Microsoft SQL Server essentially runs it's own OS, aptly named SQLOS.

[notsentient]

That's not true, SQLOS is not a wrapper for system calls or another OS running on-top of a host platform. It's more of a resource/synchronicity/management layer: http://blog.sqlauthority.com/2015/11/11/sql-server-what-is-s...