Why is the supervisor mode necessary

Supervisor mode is the automatic mode selected when a computer is powered on. It allows the initial programs executed in the computer, mainly the bootloader, BIOS and OS, to have unlimited access to the hardware. It is also the mode selected by the OS kernel for low-level tasks that require unrestricted hardware access.

Supervisor mode may provide access to different peripherals, to memory management hardware or to different memory address spaces. It provides the much-needed protective barrier between applications.

It is also capable of interrupt enabling, disabling, returning and loading of processor status. Supervisor mode can also change and create memory address spaces and also access the memory address spaces of other operations. It also has the ability to access the different data structures inside the OS. By: Justin Stoltzfus Contributor, Reviewer.

By: Satish Balakrishnan. Dictionary Dictionary Term of the Day. Gorilla Glass. And here's the kicker All exceptions on the are processed in the supervisor mode! Exception processing occurs in four main steps. In the first step, a copy is made of the status register. As soon as this is done, the S bit is asserted and, bingo, the processor is in the supervisor state.

Now it can do anything. The simple fact is that supervisor mode is used for writing operating systems and other systems software. In the early days of microprocessors there wasn't much of a need for things like supervisor mode.

The program running was in total charge of everything that happened in the processor But a funny thing happened on the way to the ST. As micros became more sophisticated they started resembling large computers more and more. The logic here is based on Murphy's Law: "If a user program can screw something up, sooner or later it will.

And once you move from single-user to multi-user systems, you have to consider how to keep individual users from stepping on each other's toes. The is an elegant architecture well suited to multi-user, multi-tasking types of applications. Remember, the is just one of a family of processors that Motorola supports. There are also an MC and MC which introduce even more elegance and a virtual machine concept.

The , for example, has an address space of two gigabytes, but a lot less physical memory is usually present. In a Y ou wouldn't want first class passengers to have to use the same bathroom as coach passengers would you? When a reference is made to memory that isn't really there, an exception is generated and the operating system sometimes known as the supervisor loads in the proper memory from a secondary storage such as a hard disk.

Even on the the supervisor state can be used by an external memory-management system. Any time the processor makes a memory reference, it classifies the type of reference being made. Recommended Articles. Article Contributed By :.

Easy Normal Medium Hard Expert. Writing code in comment? Please use ide. Load Comments. What's New. Difference between Primary Key and Foreign Key Types of Network Topology Analysis of different sorting techniques Difference between Clustered and Non-clustered index Relationship between number of nodes and height of binary tree. Most visited in Linux-Unix.