On the Intel family of microprocessors, such as the Pentium, int 80h is the assembly language op code for interrupt 80h. This is the syscall interrupt on a typical Intel-based Unix system, such as FreeBSD. It allows application programmers to obtain system services from the Unix kernel. The Unix kernel services handle such things as the opening and closing of files, accessing various devices, reading from and writing to the terminal, starting new processes, etc. Without these services, every single program would have to do it on its own. The programmer would spend so much time interfacing with the computer hardware that he/she would have little energy left to concentrate on whatever his/her software is meant to do. Such was, indeed, the case back in the 1960’s when I started programming computers. To a lesser extent, such was the case in the 1980’s when the then new personal computers used MS DOS, an operating system that provided some of these services, but not all of them. Unix existed in the 1980’s, but was used mostly on mainframe computers, not on personal computers. Nowadays, just about any personal computer can use the full power of Unix, thanks to the FreeBSD operating system.