Privileged instruction意思

"Privileged instruction" is a term used in computer science, particularly in the context of virtual memory and operating systems. A privileged instruction is an instruction that can only be executed when the processor is in a special mode, typically called "privileged mode" or "supervisor mode." This mode gives the executing program access to hardware and system resources that are not available to programs running in user mode.

In most computer systems, there are two basic modes of operation for the processor: user mode and privileged mode. User mode is the mode in which most user applications run. In this mode, the processor is restricted from accessing certain hardware and system resources, and it cannot make certain system-level changes. This is to prevent user applications from accidentally or maliciously damaging the system or other user applications.

Privileged mode, on the other hand, is the mode in which the operating system and system software run. In this mode, the processor has full access to all hardware and system resources, and it can make any system-level changes. This is necessary for the operating system to perform its duties, such as managing memory, devices, and other system tasks.

Privileged instructions are instructions that can only be executed in privileged mode. These instructions typically include instructions that allow access to system resources, such as I/O instructions, memory management instructions, and instructions that can change the processor's mode of operation.

The use of privileged instructions is an important part of the security model of most computer systems. By restricting access to these instructions, the system can prevent user applications from performing actions that could damage the system or compromise the security of other applications.