S/4 HANA Overview: Refer to this url  to have a better understanding of S/4 HANA and its related topic. ( This document is available in public domain)

HANA is High Performance analytic appliance.
HANA is the underlying in-memory database to power the applications, and S/4 is the latest package of these applications, in replacement of the traditional ECC in favor for a cloud-based IT environment.
We already know that HANA is an –

1.In Memory Database
2. Column Oriented database.
3. Massive Parallel processing of data.

The high performance of the database is because RAM is much faster than the disk. 

Column oriented database scans only the required columns and skips the unwanted columns. In one way it takes the shortcut to scan the data.
Massive parallel processing the more the resources the less time it takes to process the data and hence high performance.
SAP HANA is the underlying platform on which SAP S/4 HANA is built.