What the system actually does.
WHAT THE KERNEL DOES
Schedules processes Manages memory Controls access to devices Provides the file system Handles interrupts Enforces permissions
WHAT A SYSTEM CALL IS
A request from a program for the kernel to do something.
WHAT IT COSTS
A transition between user and kernel mode, which is not free.
WHY THAT MATTERS
Programs making many small system calls are slower than those making fewer large ones.
WHAT THE SCHEDULER DOES
Decides which process runs next, on which processor.
WHAT IT BALANCES
Fairness, responsiveness, and throughput.
WHAT A CONTEXT SWITCH COSTS
Saving and restoring state, and losing cache contents.
WHAT AN INTERRUPT IS
A hardware signal requiring attention.
WHAT KERNEL DESIGNS EXIST
Monolithic: most functionality in the kernel
Microkernel: minimal kernel, services in user space
Hybrid approaches
WHAT THE TRADE-OFF IS
Performance against isolation and reliability.
WHAT DRIVERS ARE
Code interfacing the kernel with specific hardware.
WHY THEY CAUSE SO MANY FAULTS
They run with full privilege, so a defect destabilises everything.
