Manage computer resources such as hardware and software

Provide simple and easy-to-use services for upper-level users and applications

a system software

resource manager

Provide services to upper levels

Expansion of hardware machines

concurrent

shared

virtual

asynchronous

Disadvantages: Conflict between human and machine speeds, low resource utilization

Single-channel batch processing system (offline input and output)

Multi-channel batch processing systems (operating systems begin to appear)

Advantages: Provide human-computer interaction function

Disadvantages: Unable to prioritize urgent processes

Hard real-time operating system

Soft real-time operating system

Advantages: Urgent processes can be prioritized

Privileged instructions

unprivileged instructions

Kernel state (tube state)

User mode (eye mode)

Rely on the program status word register to determine the status

Kernel program (the kernel of the operating system)

Applications (running on top of the operating system)

The operating system kernel forcibly takes back control of the CPU

Let the CPU change to kernel state

Interrupt (external interrupt signal)

Exception (internal interrupt signal)

Check interrupt signal

Find the corresponding interrupt handler (handled through the interrupt vector table)

Some library functions are further encapsulation of system calls

Some library functions do not use system calls

Passing on parameters

stuck in instruction

System call requests are processed by the operating system kernel program

Return to application

The main functional modules of the operating system are used as the system kernel and run in the kernel state.

Advantages: high performance, low switching frequency between core mode and user mode

Disadvantages: Large amount of kernel code, difficult to maintain, messy structure

Linux, UNIX, Windows

Keep only the most basic functions in the kernel

Advantages: less kernel code, clear structure, easy to maintain

Disadvantages: Need to frequently switch between user mode and kernel mode, low performance

Mac

The kernel is divided into multiple layers, and each layer can call the interface of the next layer in one direction.

Advantages: Easy to debug and verify, bottom-up layer-by-layer debugging and verification

Disadvantages: low efficiency, cannot be called across layers, and difficult to reasonably define the boundaries of each layer

Divide the kernel into multiple modules, and each module works collaboratively (kernel = main module + loadable kernel)

Advantages: Supports dynamic loading of new kernel modules, modules can directly call each other, high efficiency

Disadvantages: Interdependence between modules, difficult to debug and verify

The kernel is responsible for process scheduling, process communication and other functions. The outer core is responsible for allocating unabstracted hardware resources to user processes, and the outer core is responsible for ensuring the security of resource use.

Advantages: The outer core can directly allocate hardware resources to user processes, and user processes can use resources more flexibly, reducing the mapping layer of virtual hardware resources and improving efficiency.

Disadvantages: Reduce system consistency and the system becomes more complex

Find the C drive location through the master boot record, and import the C drive boot record into RAM

Runs directly on the hardware and can directly control and allocate resources

Can directly allocate physical hardware without abstraction

Runs at the highest privilege level and can execute advanced instructions

Advantages: better performance, more virtual machines that can be supported

Disadvantages: poor mobility

Runs on HostOS and relies on HostOS to allocate physical resources to it

GuestOS has its own virtual disk - effectively a large file in HostOS that can only allocate virtual memory

Runs in user mode, partially runs in kernel mode

Advantages: good migration

Disadvantages: Poor performance, small number of supported virtual machines