First: operating system principle series operating system preliminary understanding
Types of logical structures
- Integral structure
Build with modules as the basic unit
Disadvantages: Information transfer at will, maintenance and update difficult
- Hierarchical structure
For example, in the TCP/IP protocol stack, all function modules are arranged in multiple layers according to the call order, and only one-way dependencies or one-way calls exist between adjacent layers
Advantages: clear structure, avoid circular call, the whole problem is localized, the correctness of the system is easy to ensure, conducive to the maintenance of the operating system, expansion, transplantation
- Microkernel structure (B/S,C/S)
Operating system = microkernel + external server microkernel: small enough to provide the most basic core functions and services of the OS, generally used to implement hardware-related processing, to achieve some basic functions responsible for communication between the client and the server
External server: performs most of the OS service functions and waits for applications to make requests. It is composed of multiple servers or processes and runs in user mode in the form of processes
The CPU state
The most basic hardware structure that supports an operating system
CPU, memory, interrupt, clock
The CPU state
CPU operating status, description of resource and instruction permissions
The classification of the state
Nuclear: Ability to access all resources and execute all hypervisor /OS kernels
User mode (user mode) : can access only some resources, other resources are limited, user program
Tube state: between the core state and user state
Conversion between user state and core state
- Transition from user state to core state
The user requests the OS to provide services
Send the interrupt
The user process has an error
The user mode attempted to execute the privileged instruction
- The case of transition from nuclear state to user state
Interrupt return
Hardware and OS observations of CPU
Hardware identifies CPU states by state
The OS distinguishes CPU states by processes
Intel CPU state
The Intel CPU has four privilege levels: RING0,RING1,RING2, and RING3. Windows uses only two levels of RING0 and RING3. RING0 is only used by operating systems, and RING3 is used by anyone. If a normal application attempts to execute a RING0 instruction, Windows displays an “illegal instruction” error message. Ring0 indicates the CPU running level. Ring0 is the highest level, followed by Ring1, and ring2…
Procedure A checks permission when accessing procedure B. Request privilege descriptor privilege level
memory
A unit that stores programs and data
Classification: by memory (semiconductor memory) read and write working mode RAM ROM
By storage element material Semiconductor memory (common main memory) Magnetic memory (disk, tape) optical memory (CD)
Follow the association with the CPU
Main storage: directly exchanges information with the CPU Secondary storage: Cannot directly exchange information with the CPU
Ideal storage system
Large speed, large capacity, low cost
Physical storage system
- register
- cache
- Main memory
- Auxiliary storage
Working principles of a tiered storage system
The order in which the CPU reads instructions or data
1) Access cache (hit,hit)
2) Access memory (MISS, MISS)
3) Access secondary storage (missing page, PAGE_FAULT)
The interrupt mechanism
Definition: a process or mechanism by which the CPU responds to a sudden external event. When the CPU receives an external signal (interrupt signal), it stops working, switches to the external event, and returns to the original work break point (breakpoint) after processing. The occurrence of the event changes the control flow of the processor
The difference between interrupts and exceptions is passive and active 
Purpose: To realize concurrent activities, real-time processing, automatic fault processing Interrupt source: the event that causes the system interruption is called the interrupt source
Interrupt types: forced interrupts (the program is not expected) and voluntary interrupts (the program is expected), external interrupts and internal interrupts
Breakpoint: The place where the program breaks and the address (CS:IP) at which the next line of instruction is to be executed
Site: the information set on which the program runs correctly. There are two processing processes for the site. One is the protection of the site: before entering the interrupt service program, stack; the other is the recovery of the current data, after exiting the interrupt service program
Essence: switching instruction execution addresses, switching CPU states, working for field protection and recovery, and parameter passing (communication)