Preface

Kernel state and user state .

One 、 Kernel state and user state

In order to prevent the operating system and key data from being destroyed by user programs , The execution state of the processor is divided into kernel state and user state . The user program runs in user mode , The operating system kernel runs in kernel mode .

Kernel state is Operating system management program The state of execution , Be able to execute... Including privileged instructions All instructions , Be able to access the system All storage space .
User status is User programs The state of execution , Cannot execute privileged instructions , Only user address space can be accessed .

Two 、 Switching between kernel state and user state

Switch from user state to kernel state ： system call 、 Exceptions and external interrupts .

（1） The system call is the function of the operating system Minimum functional unit , It's provided by the operating system The user interface , The system call itself is a Soft interrupt .

（2） Exceptions are also called Internal interruption , yes Caused by mistake Of , If the file is damaged 、 Page missing fault, etc .

（3） External interruption is notified by two signal lines Processor peripherals The state of change , Belong to Hard interrupt .

3、 ... and 、 Concurrency and parallelism

（1） parallel ： Strictly physical At the same time . Such as multi-core CPU.

（2） Concurrent ： Macroscopically, it seems that the two programs are running at the same time , It's actually Alternate operation Of . Such as single core CPU Multitasking on .