Multitasking is the ability of an operating system to run multiple tasks by rapidly switching the CPU between them. This switching, known as context switching, gives each task a small time slice, creating the illusion that tasks are running simultaneously and ensuring smooth system performance.
- Allows multiple tasks to run at the same time
- Uses context switching to share CPU time
- Provides each task a small time slice
- Improves system efficiency and user experience
Works of Multitasking
Multitasking is achieved through:
- Time Slicing: Dividing CPU time among tasks in small slices.
- Context Switching: Saving the state of one task and restoring another’s state to resume execution seamlessly.
- Resource Management: Efficient allocation of memory, I/O devices, and CPU cycles across multiple tasks.
Types of Multitasking
Multitasking can be classified into two types based on the execution unit:
- Process-based Multitasking
- Thread-based Multitasking
Now lets discuss these two in brief:
Process Based Multitasking
In process-based multitasking, two or more independent processes run concurrently. Each process is self-contained with:
- Its own memory space (address space)
- Its own code, data, and system resources
- Its own Process Control Block (PCB)
Key Features
- Isolation: Each process runs independently, preventing interference.
- Heavyweight: Requires more overhead due to separate memory allocation.
- Slower Communication: Inter-Process Communication (IPC) mechanisms (pipes, message queues, shared memory) add complexity.
- Better Security: Faults in one process do not affect others, ensuring stability.
Benefits
- Strong fault isolation: one crashed process does not affect others.
- High robustness: ideal for untrusted or independent applications.
Limitations
- Memory overhead due to separate address spaces.
- Higher context switching cost than threads.
- Complex IPC, which increases communication overhead.
Example: Running a music player while using a web browser.
Both are separate processes with independent memory and resources.
Thread Based Multitasking(Multithreading)
In thread-based multitasking, multiple threads run within a single process. Threads share:
- The same address space, code, and data
- But each has its own stack and execution context
Key Features
- Lightweight: Faster to create and manage compared to processes.
- Shared Memory: Enables direct communication between threads.
- Efficient Synchronization: Achieved using primitives like locks, semaphores, and condition variables.
- Scalable: Threads can exploit multiple CPU cores for parallelism.
Benefits
- Lower overhead in terms of memory and context switching.
- Fast communication between threads through shared memory.
- Improved responsiveness within applications.
Limitations
- Lack of isolation: A faulty thread may crash the entire process.
- Synchronization issues: Requires careful handling to avoid race conditions and deadlocks.
- Complex debugging: Concurrency issues make testing and debugging harder.
Example
- In a web browser, one thread handles navigation while another downloads files.
- In MS Word, one thread processes text input while another performs spell-check.