I have a question related to the API. I am not sure if it is part of the operating system or not. I am confused because AFAIK each operating system has a specific API.
APIs are available for both desktop and mobile operating systems. The Windows API, for example, provides developers with user interface controls and elements, such as windows, scroll bars, and dialog boxes. It also provides commands for accessing the file system and performing file operations, such as creating and deleting files. Additionally, the Windows API includes networking commands that can be used to send and receive data over a local network or the Internet.
Every Operating System has a set of API for developers to implement some sort of application.