Was the first operating system to integrate security as its core functions.

Multics

Explanation:

The creation of the MULTICS operating system (MULtiplexed Information and Computing Service). This was a joint project carried out by the MIT (Massachusetts Institute of Technology), Bell Laboratories and General Electric. The idea was to distribute computer service to an entire city, in the same way that electricity is distributed using a machine with two processors and 256K 36-bit words (just over 1Mb) as support. MULTICS did not achieve its objectives, although it has been used in different organizations (especially universities). Yes, it is important to note that one of the Bell Laboratories scientists, Ken Thompson, rewrote a single-user version of MULTICS, which he sorely called UNICS.