As a SQL Server DBA or developer here is what you should know about memory-optimized tables (in-memory tables):

• Introduced in SQL Server 2014
• Primary store is main memory, second copy maintained on disk to achieve durability
• Handled by in-memory OLTP, a memory optimized database engine integrated with SQL Server engine
• Fully durable, ACID transactions. Supports delayed durability for better performance (risk losing  committed transaction that have not been saved to disk)
• SQL Server supports non-durable memory optimized tables (not logged and data not persisted to disk) – no recovery option in case of disk crash
• No-lock concurrency eliminates blocking and achieves better performance. Concurrency handled through row versioning. 
• Not organized in pages and extents, memory-optimized tables are a collection of row versions and a row version is addressed using 8-byte memory pointers
• Data in memory-optimized tables can be accessed:
• (most efficient) Through natively compiled SPs (the limitations is that natively compiled SPs can only access in-memory tables)
• Through interpreted t-sql inside a standard SP or through ad-hoc t-sql statements.