Operating Systems · Foundations

System calls and kernel mode

The controlled doorway, a trap into kernel mode, a program uses to ask the OS to do something on its behalf.

Also known as: syscalls, user mode, kernel mode, traps.

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• What an operating system does: The OS as the layer that turns raw, shared hardware into a clean, protected abstraction for programs.

Leads to

• The process abstraction: A running program's isolated illusion of its own CPU and memory, tracked by the OS as a process control block.
• I/O devices and interrupts: How the OS talks to devices, through polling, interrupts, or DMA, without the CPU babysitting every transfer.
• Protection and security basics: The privilege levels and access checks that keep one process from reading or corrupting another's memory.

Related topics

• Protection and security basics: The privilege levels and access checks that keep one process from reading or corrupting another's memory.