OSinterfaces

OS interfaces are the points of interaction between an operating system and software components or users. They specify how programs request services from the kernel, how applications perform common tasks, how hardware is managed, and how information is presented to users.

Major categories include system call interfaces, application programming interfaces and libraries, kernel-to-driver interfaces, interprocess communication primitives, and file system interfaces. The system call interface defines entry points for user-space programs to request services from the kernel, such as process creation and I/O. APIs and libraries expose higher-level, portable functions standardized by POSIX on Unix-like systems or the Windows API on Windows. Kernel-driver interfaces govern communication between the kernel and device drivers. IPC primitives provide pipes, queues, shared memory, and sockets. File system interfaces define how files are accessed and named, typically via a virtual file system layer.

User interfaces include command-line interfaces and graphical user interfaces that let users control the system or run programs. Scripting interfaces and shells such as Bash or PowerShell provide programmable access to OS features, enabling automation and batch processing. Together, these interfaces allow both humans and software components to operate the system efficiently.

Examples include POSIX on Unix-like systems and the Windows API for Windows. macOS provides Cocoa atop the Darwin kernel. Modern OS designs emphasize layered architectures with clear user-space and kernel-space separation, balancing abstraction, performance, and security, while preserving backward compatibility for applications and drivers.