[AaronFriel]

Both are true! MS SQL Server is a "true MVCC" database (no-true Scotsman?) and you are correct. SQL Server supports snapshot/MVCC isolation for transactions, but it must be enabled. They are determined to maintain 20 years of backward compatibility, and while I think that's wrong, they leave snapshot isolation disabled by default.

https://msdn.microsoft.com/en-us/library/ms173763.aspx

[serguzest]

It uses tempdb for tracking versions, it is not true mvcc in the engine.

[br1]

That's an internal detail. It's much cleaner than postgresql that leaves old tuples in disk and has to vacuum them later.

[greggyb]

It also offers an optimized in-memory transactional engine that is lockless and compiles stored procedures to native code.