1. System call
2. System calls have the following functions and features:
The operating system manages the hardware for us, and user-mode processes do not have to deal directly with hardware devices.
Greatly improve the security of the system. If the user mode process directly interacts with the hardware device, it will cause security risks and may cause the system to crash.
Make user programs portable. The user program and the specific hardware have been decoupled and replaced with an interface (api), and there will be no close relationship, which is convenient for porting between different systems.
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