An in-memory database Vs a database management system in our data-driven era

For those who are unfamiliar, it is indispensable to recall that, an in-memory database (IMDB, also main memory database system or MMDB or memory resident database) is a system that majorly relies on the computer's main memory to store data and is different from a database management system which uses a disk storage mechanism. 

Simpler internal optimization algorithms and fewer CPU instructions make main memory databases relatively faster than disk-optimized databases.