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Chapter 14 – Context Switching

Core idea

A context switch saves the state of one execution unit and restores another.

What gets saved

• Registers
• Program Counter
• Stack Pointer
• CPU flags
• Memory mappings (if process switch)

Types

• Thread switch – cheaper
• Process switch – more expensive

When switches happen

• Time slice expired
• I/O blocking
• Higher-priority process ready
• System call

Cost

• No useful work done
• Cache pollution
• TLB flush (for process switches)

Exam angle

• Context switches are overhead
• Threads reduce switching cost