Every memory address used by a process should be first checked to see whether it falls within the range of memory area that is allocated to the process. Two special purpose registers-lower bound register (LBR) and upper bound register (UBR) are used to implement memory protection.
How is memory protected?
Virtual memory makes it possible to have a linear virtual memory address space and to use it to access blocks fragmented over physical memory address space. Most computer architectures which support paging also use pages as the basis for memory protection.
What is the fence register used for?
A fence register derives the boundary between operating system and users. The fence cannot prevent penetration of one user into the area of another user.
What is base and limit register?
The base register holds the smallest legal physical memory address; the limit register specifies the size of the range. For example, if the base register holds 1000, and limit register is 800, then the program can legally access all addresses from 1000 through 1800 (inclusive).
What is the fence register?
Variable Fence Register. A fence register protects only in one direction. In other words, an operating system can be protected from a single user, but the fence cannot protect one user from another user.
What is main memory protection?
Memory protection is a way to control memory access rights on a computer, and is a part of most modern instruction set architectures and operating systems. The main purpose of memory protection is to prevent a process from accessing memory that has not been allocated to it.
What else is a command interpreter called?
Command interpreter is an important part of any operating system. It provides an interface between the user and the computer. A command interpreter is often also called a command shell or simply a shell.
Which of the following is not the state of process?
Which of the following is not the state of a process? Explanation: There is no process state such as old. When a process is created then the process is in New state. When the process gets the CPU for its execution then the process is in Running state.
Which is real time operating system?
A Real Time Operating System, commonly known as an RTOS, is a software component that rapidly switches between tasks, giving the impression that multiple programs are being executed at the same time on a single processing core.
Why relocation register is used?
Relocation registers used to protect user processes from each other, and from changing operating-system code and data. – Base register contains value of smallest physical address – Limit register contains range of logical addresses – each logical address must be less than the limit register.