Context switching in Operating Systems - Step-by-Step Execution

Concept Flow - Context switching

CPU running Process A

↓

Interrupt or Scheduler Trigger

↓

Save Process A state

↓

Load Process B state

↓

CPU runs Process B

↓

Repeat when next switch needed

The CPU stops running one process, saves its state, loads another process's state, and runs it.

Execution Sample

Operating Systems

Process A running
Interrupt occurs
Save A's state
Load B's state
Process B running

Shows the steps when CPU switches from Process A to Process B.

Analysis Table

Step	Action	Process State	CPU Activity
1	CPU runs Process A	Process A running	Executing Process A instructions
2	Interrupt occurs	Process A state saved	Preparing to switch
3	Save Process A state	Process A state saved in memory	CPU ready to load next process
4	Load Process B state	Process B state loaded from memory	CPU loads Process B context
5	CPU runs Process B	Process B running	Executing Process B instructions
6	Next interrupt or scheduler trigger	Process B state saved	Preparing next switch

💡 Execution continues switching processes as interrupts or scheduler triggers occur

State Tracker

Variable	Start	After Step 2	After Step 4	After Step 5
CPU Current Process	Process A	Saving Process A	Process B loaded	Process B running
Process A State	Running	Saved	Saved	Saved
Process B State	Not loaded	Not loaded	Loaded	Running

Key Insights - 3 Insights

Why does the CPU save the current process state before switching?

Because the CPU must remember where the current process left off to resume it later, as shown in step 3 of the execution_table.

What happens if the CPU does not load the next process state correctly?

The CPU would not have the correct information to run the next process, causing errors or crashes, as implied in step 4.

Is the CPU running two processes at the same time during context switching?

No, the CPU runs only one process at a time; context switching quickly changes which process runs, as shown by the CPU Current Process variable in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is happening to Process A's state?

A It is deleted

B It is loaded to CPU

C It is saved to memory

D It is running

💡 Hint

Check the 'Process State' column at step 3 in execution_table

At which step does the CPU start running Process B?

A Step 2

B Step 5

C Step 4

D Step 3

💡 Hint

Look at the 'CPU Activity' column in execution_table for when Process B runs

If the CPU did not save Process A's state, what would happen in the variable_tracker?

A Process A State would remain 'Running' after step 3

B Process B State would be 'Running' from start

C CPU Current Process would be 'Process B' from start

D Process A State would be 'Deleted'

💡 Hint

Refer to the 'Process A State' row in variable_tracker after step 2 and 3

Concept Snapshot

Context switching is when the CPU stops running one process,
saves its state, loads another process's state, and runs it.
This allows multitasking by sharing CPU time.
Key steps: save current state, load next state, run next process.
CPU runs only one process at a time but switches quickly.

Full Transcript

Context switching is a process in operating systems where the CPU stops running the current process, saves its state, and loads the state of another process to run it. This allows multiple processes to share the CPU by switching between them quickly. The steps include the CPU running a process, an interrupt or scheduler trigger causing a switch, saving the current process's state, loading the next process's state, and then running the next process. Variables like the CPU's current process and each process's state change during these steps. Understanding these steps helps clarify how multitasking works in computers.