What is a kernel, and what services does it provide to user processes?
What is Kernel?
A kernel is the core component of an operating system that acts as an interface between the hardware and software layers of a computer system. It provides various services to user processes, including process management, memory management, device management, and security.
Process management
The kernel manages the creation, scheduling, and termination of processes in the system. It provides a process table that contains information about each running process, including the process state, priority, and resource usage.
Example
When a user opens an application, the kernel creates a new process for that application and schedules it to run on the CPU. The kernel also manages the termination of the process when the user closes the application.
Memory management
The kernel manages the allocation and deallocation of memory to processes. It provides virtual memory services that allow processes to use more memory than is physically available in the system. The kernel also implements memory protection mechanisms that prevent processes from accessing memory that belongs to other processes.
Example
When a user opens a file, the kernel allocates memory to store the file contents and maps the memory to the process address space. This allows the user process to access the file contents as if they were in memory, even if the file is larger than the available physical memory.
Device management
The kernel manages the access to input/output (I/O) devices in the system, such as disks, printers, and network cards. It provides device drivers that interface with the hardware and provide a standardized interface to user processes. The kernel also handles device interrupts, which occur when a device needs attention from the CPU.
Example
When a user sends a print job to a printer, the kernel sends the job to the printer driver and waits for the driver to signal that the job is complete. The kernel also handles interrupts from the printer, such as when the printer is out of paper.
Security
The kernel provides various security mechanisms to protect the system from unauthorized access and malicious software. It implements access control policies that restrict access to system resources based on user identity and permissions. The kernel also provides process isolation mechanisms that prevent one process from accessing the memory or resources of another process.
Example
When a user logs into the system, the kernel authenticates the user's credentials and assigns a unique user ID to the user's processes. The kernel then enforces access control policies that restrict the user's access to system resources based on the assigned user ID and permissions.