As The Walking Cat discovered by taking a peek into the public preview of SQL Server on Linux released last week, Microsoft seemed to be using the Microsoft Research "Drawbridge" technology to bring SQL Server to Linux. Drawbridge is an adaptation of the Library OS concept on which Microsoft Research has been working for the past several years. It's a form of virtualization specifically for application sandboxing. Drawbridge played a role in getting the Bash shell to run on Windows 10, too.
A Microsoft spokesperson confirmed that Drawbridge, was, indeed, at the core of how Microsoft got SQL Server running on Linux.
"To enable SQL Server on Linux we have created the SQL Platform Abstraction Layer (SQLPAL), which evolved from Drawbridge," the spokesperson said when I asked.
So what about Microsoft's claim that "all features of the SQL Server Next database will be available in Linux and Windows"?