Device operating systems hold a unique place in the data ecosystem. They are the connection between user interfaces and sensors on the one hand, and applications and networks on the other. They provide the linkages that allow apps to store and access local data and they provide the intelligence that makes each device an individual. Most importantly, by occupying this central role in the data-scape, operating systems often take on the role of overseer and arbiter in the many interactions between the systems and software they connect.
To perform its function, the operating system (OS) must, of necessity, catalogue the capabilities, identities, and permissions allotted to the device, its peripherals, and any loaded applications - things that together uniquely identify your device from the millions of others out there. The OS knows who you are, and it sees the comings and goings of the packets and bytes that travel between apps, in and out of memory, and across the network to the world outside - even if it may be unaware of their actual content. For this reason, it is also the most tightly watched part of the data chain, constantly attacked by intruders and constantly updated by its defenders.
In most cases, the OS functions almost autonomously, simply managing the plumbing and keeping the data flowing as instructed. However, given its central role in data security, managing peripheral and application permissions, and generally policing the many data interactions taking place, it can be a very rich source of data if misconfigured or compromised. A properly implements OS is the gatekeeper that keeps apps - and the data they hold - compartmentalized and safe from unauthorized access.