What Is Supervisor Call?

A supervisor call is like a phone call to the boss. When you do a supervisor call, your computer's processor requests its operating system, asking it to transfer control over to the supervisor program—just an application that runs in the background on any computer. From there, the operating system will perform whatever task you've asked it to do and then return control to your program. Supervisor calls are sometimes referred to as system calls or macros because they're implemented through language functions. Supervisors' calls are the secret sauce of your computer's operating system. They're like a secret handshake between you and your computer: they allow you to access the super-important stuff that makes your computer tick. How do they work? Well, imagine that you're at a party and someone asks you to dance at the table. You'd probably say no—but if it was a boss or family member who asked, there's a good chance you'd do it anyway. That's how supervisor calls work! When your manager or mom asks for something, you have to do it—even if it means interrupting what you're doing to switch into the supervisor call mode. Supervisory calls are like the little things in life that improve big things. They're the little touches that make you feel like a person is waiting to help you—that make you feel like someone is there, ready to lend a hand. And when it comes to operating systems? Well, they're pretty much mandatory. The majority of operations that interact with the system require permissions not available to user-level processes. For example, in Unix- and POSIX-compatible operating systems, several macros simplify the supervisor call procedures. These include widespread system calls such as open, write, read and close. Every new operating system houses hundreds of these little helpers!