Memory protection in operating system pdf

Base register - it contains the smallest legal physical memory address for a process. Limit register - it holds the size of the process. When a process is loaded into memory, the base register is initialized with the beginning address of the process and the limit register is initialized with the size.

Memory outside the defined range is secluded because the CPU checks that every address generated by process falls within the memory range defined by the values stored in base and limit registers, as shown in Figure drawn below. Figure Hardware address protection with base and limit registers.

In Figure drawn below we use an example to illustrate how the concept given above works. The base and limit registers are initialized to describe the address space of a process. The process begins at memory location and its size is bytes supposing that memory is byte addressable. Loading the base and limit registers are the privileged instructions.

Email based Operating System assignment help - homework help at Expertsmind. Are you searching Operating System expert for help with Memory Protection questions? Memory Protection topic is not easier to learn without external help? We at www. Live experts are available for 24x7 hours helping students in their Memory Protection related problems.

We prepare quality content and notes for Memory Protection topic under operating system theory and study material. These are avail for subscribed users and they can get advantages anytime. Why Expertsmind for assignment help. This prevents applications from seizing control of an inordinate amount of memory and possibly causing damage that negatively impacts other applications that are currently in use, or even creating a loss of data that is saved on the hard drive.

In many operating systems, this is managed by segmenting the memory for use by all open applications, ensuring that each has enough to operate properly without creating issues with the other running applications. While there is a separation of protection and security within an operating system, the use of memory protection does aid in the proper function of the security protocols inherent within the system. This means that even as the security features are attempting to prevent a bug from causing damage to data or to the files that support the operating system, the memory protection is preventing the bug from accessing a larger share of memory and creating operational issues that would slow down the security initiatives.

Over the years, memory protection has become increasingly sophisticated. This rule applies to all descriptors except the LDT descriptor.

Memory protection by keys privilege level is used in most modern computers with paged memory organization and its dynamic distribution between the parallel running programs. It is based on the use of special codes levels to verify compliance between using of arrays of memory cells and the number of a running program.

Each working program is given a special key by the OC - the key of the program. All selected for this work program pages are marked by the same page key, or security key. As a security key binary program numbers is usually specified. During the appeal to the OP takes place a comparison between the key of a running program with the protect keys of the respective pages of memory. Appeal is permitted only in case of the compared key codes coincidence. Memory protection by keys applies not only during the work with OD and processor, but also during the exchange of information with TSD through input-output lines.

In that case are used channel keys instead of the programming keys. Bit key code is determined by the maximum number of concurrently running programs. The idea of the method is that there are injected two boundary registers, indicating the upper and lower boundaries of the memory area where the program has an access to.

For each memory access it is checked whether the address is used to set the boundaries. In case of leaving abroad to the memory access there is suppressed and formed the interrupt request, that is transmitting the control to the operating system.

The contents of the boundary registers are set by the operating system before the active cycle begins for the next target program. If you use a base register, it simultaneously determines both limits for the dynamic memory allocation.