Beginner operating system, concept carding (updating)

1. What is the function of interruption

Interrupt is a mechanism commonly used in computer systems, which is used to respond to external events in a timely manner during computer processing tasks, such as input device input, timer arrival, etc., so as to process these events in a timely manner. Interrupt can suspend the currently executing program and execute specific interrupt service routines. These service routines can read device data, update system status, perform error handling, etc., and finally return to the interrupted program to continue execution.

The role of interruption mainly has the following aspects:

1. Improve the response speed of the system: By responding to external events in time, the waiting time can be reduced, and the response speed and real-time performance of the system can be improved.
2. Improve system resource utilization efficiency: The interrupt mechanism can avoid CPU idling and improve system resource utilization efficiency.
3. Simplify programming: The interrupt mechanism can help programmers decompose complex system processing tasks into smaller modules, simplify programming difficulty, and improve code maintainability and reusability.
4. Improve system reliability: Through the interrupt mechanism, the system can handle errors and abnormal situations, and improve system reliability and stability.

2. What is the five-state model, let me introduce it in detail

The five-state model refers to the five basic states of processes in the operating system, including:

1. Creation state (New): Indicates that the process is being created, but system resources have not been allocated, such as memory, file handles, etc.

2. Ready state (Ready): Indicates that the process has allocated the necessary system resources and is waiting to allocate processor resources to run.

3. Running: Indicates that the process has acquired processor resources and is executing.

4. Blocked state (Blocked): Indicates that the process cannot execute because it is waiting for a certain event to occur, such as waiting for I/O to complete, waiting for a semaphore, and so on.

5. Terminated: Indicates that the process has finished running and released all system resources.

This model is usually used to describe the running state of a process in an operating system and the transition relationship between states. The process enters the ready state from the creation state, waiting for the allocated processor resources to run. When a process acquires processor resources, it enters the running state. If the process needs to wait for some event (such as I/O completion), it will enter the blocking state and wait for the event to occur. When the event occurs, the process enters the ready state again, waiting to be allocated processor resources to run. When the process finishes running, it enters the terminated state, freeing all system resources.

The five-state model is the basis of process management in the operating system, which describes the running state of the process in the system and the transition relationship between states. Through the monitoring and scheduling of process status, the operating system can effectively manage processes, optimize the use of system resources, and improve system performance and reliability.

 3. The concept and difference between process switching and mode switching

Both process switching and mode switching are important concepts in the operating system. There are differences between the two. The following is a brief introduction:

1. Process switching

Process switching means that in the operating system, when a process is suspended or blocked, the system needs to switch to another process for execution. Process switching is one of the core mechanisms in the operating system. It implements the basic function of multitasking, enables multiple processes to share CPU resources, and improves system utilization.

In the process of process switching, the operating system needs to save the context information of the current process, including the value in the CPU register, stack pointer, program counter, etc., so as to resume the execution of the process later. At the same time, the operating system also needs to allocate CPU resources to another process and restore the context information of the process so that the process can continue to execute.

2. Mode switching

Mode switching refers to switching between operating modes of the CPU, such as switching from user mode to kernel mode. In an operating system, user programs usually run in user mode, while kernel code runs in kernel mode. Programs in user mode can only access their own memory space and CPU registers, but cannot access the core data structures and system resources of the operating system, which can ensure system security. The code in kernel mode can access all resources and data structures of the operating system, and perform core operations such as system calls and interrupt processing.

During the mode switching process, the CPU needs to save the context information of the currently running program and switch to the kernel mode to run. In kernel mode, the CPU can perform core operations such as system calls and access system resources. After completing these operations, the CPU returns the execution right to the user program, performs mode switching, restores context information, and allows the user program to continue executing.

In short, both process switching and mode switching are very important concepts in the operating system. Both need to save context information and switch to different execution environments to achieve different functions. Process switching realizes multi-task processing, so that multiple processes can share CPU resources; while mode switching realizes the security isolation between the operating system and user programs, ensuring the security of the system.

4. What does IDT (Interrupt Descriptor Table) refer to in the operating system

IDT (Interrupt Descriptor Table) is an important data structure in the operating system, which is used to store and manage the entry addresses of interrupt and exception handlers. IDT is a table composed of descriptors, each descriptor corresponds to an interrupt or exception, and stores information such as the entry address of the corresponding handler and the privilege level of the handler.

In the given code, the IDT table is initialized to a set of entry addresses of exception and interrupt handlers corresponding to different exception or interrupt types. For example, exception number 0 is "division error exception", interrupt number 1 is "alarm clock 1", interrupt number 3 is "clock interrupt" and so on.

When the CPU detects an interrupt or an exception, it will look up the IDT table, obtain the corresponding descriptor according to the interrupt or exception type, thereby determine the entry address of the handler, and then jump to the address to execute the corresponding handler. These handlers are usually written by the operating system to handle specific exceptions or interrupts, for example, handling division by zero errors, clock interrupts, hard disk reads and writes, and so on.

Therefore, the IDT table is one of the very important data structures in the operating system. It provides a mechanism for the operating system to manage and respond to interrupts and abnormal conditions, ensuring that the system can run stably.

5. The X process is about to issue the No. 4 system call. It is the same as the No. 5 system call issued by the Y process before, but the corresponding devices are different. Can these two devices work at the same time?

The answer to this question needs to be determined according to the specific design and implementation of the system. Here are some possible situations:

If the system supports multi-threading or multi-processing, then X and Y can run concurrently, and the system calls issued by them can also be executed at the same time. In this case, the equipment corresponding to X and Y may be occupied at the same time, but the system will schedule according to the scheduling algorithm and priority to ensure the reasonable use of the equipment.

If the system does not support multi-threading or multi-processing, then X and Y can only run sequentially, and the system calls they issue can only be executed sequentially. In this case, it is impossible for the devices corresponding to X and Y to work at the same time.

In addition, even if the system supports multi-threading or multi-processing, some devices may not support concurrent operations, depending on the hardware characteristics of the device and the implementation of the driver. In this case, the system may use mechanisms such as mutual exclusion or semaphores to avoid conflicting access to the device.

In short, whether the devices can work at the same time depends on the design and implementation of the system, as well as the hardware characteristics of the device and the implementation of the driver. In actual development, it is necessary to carry out testing and optimization according to specific conditions in order to improve the performance and reliability of the system.