Järjestelmäkutsuiksi

Järjestelmäkutsuiksi, in Finnish, translates to "system calls" in English. System calls are the fundamental interface between a user-level program and the operating system kernel. When a program needs to perform an operation that requires privileged access to hardware or kernel resources, such as reading a file, creating a process, or communicating with other processes, it makes a system call.

The process typically involves the user program loading arguments into specific registers or memory locations and then executing a special instruction that triggers a trap or software interrupt. This interrupt transfers control to the operating system kernel. The kernel then examines the system call number to determine which operation the user program requested. It performs the requested operation, often with elevated privileges, and then returns control to the user program, usually with a return code indicating success or failure.

System calls are essential for the security and stability of an operating system. By mediating access to resources through system calls, the kernel can prevent user programs from directly manipulating hardware, which could lead to data corruption or system crashes. Common examples of system calls include `open` for opening files, `read` and `write` for file I/O, `fork` for creating new processes, and `exit` for terminating a process. Each operating system provides its own set of system calls, although POSIX standards aim to provide some level of compatibility across different Unix-like systems.