Operating Systems Notes
Subject Overview
Operating Systems covers OS fundamentals and process/
Subject at a glance
4
Units
37
Topics
5
Credits
4
Infographics
Unit-wise Syllabus
4 units — open any unit for detailed topic-wise notes, diagrams and important exam questions
- Application vs system programs
- OS functions and classification (multi-user, multiprogramming, multiprocessing, time-sharing, multi-threaded)
- subsystem layers
- bootstrap
- protection and security
- program vs process
- process context/address space/state management
- thread management benefits and synchronization
- 1. New: Process is created
- 2. Ready: Waiting for the CPU
- 3. Running: Instructions executing
- 4. Waiting: For I/O or an event
- 5. Terminated: Finished
Study guide
This unit introduces the OS: application versus system programs, OS functions and types, subsystem layers, bootstrap, protection and security, programs versus processes, process context and states and thread management. Learn the five-state process model.
- Preemptive vs non-preemptive scheduling
- context switching
- scheduling schemes
- multi-processor and thread scheduling
- message passing and shared memory IPC models
- pipes
- FIFO and sockets
FCFS
No
Simple; convoy effect
SJF
Either
Lowest average waiting time
Priority
Either
Risk of starvation; use ageing
Round robin
Yes
Time quantum; fair for time-sharing
Study guide
You study scheduling (preemptive and non-preemptive), context switching, scheduling schemes, multiprocessor and thread scheduling and inter-process communication by message passing and shared memory, with pipes, FIFOs and sockets. Practise scheduling problems with Gantt charts.
- Address binding
- relocation
- loading
- linking
- memory sharing and protection
- paging and segmentation
- virtual memory (demand paging, performance, page replacement, thrashing)
- I/O devices and controllers
- device drivers
- disk scheduling and management
Divides memory into
Fixed-size pages and frames
Variable-size logical segments
Fragmentation
Internal
External
Programmer sees
One linear address space
Separate segments: code, data, stack
Table
Page table
Segment table
Study guide
You study address binding, relocation, loading and linking, memory sharing and protection, paging and segmentation, virtual memory (demand paging, page replacement, thrashing), I/O devices, drivers and disk scheduling. Practise page replacement algorithms by hand.
- File operations
- access methods
- directory structures and management
- remote file systems
- file protection
- security environments
- unauthorized use
- denial of service
- access control and authentication
- application security
- viruses and anti-virus
- firewalls
Authentication
Passwords, biometrics, OTP
Access control
Permissions and access lists
Anti-malware
Virus and worm defence
Firewall
Filters network traffic
Updates and audit
Patches and logs
Study guide
You study file operations, access methods, directory structures, remote file systems, protection, security environments, authentication, viruses, antivirus tools and firewalls. Compare the directory structures with diagrams.
Why Operating Systems Matters
The operating system is the heart of every computer, and its concepts are asked in almost every IT interview and competitive exam. They also lead to careers in systems, cloud and cybersecurity.
How to Prepare for Operating Systems
- Practise scheduling and page replacement numericals.
- Make notes on deadlock, paging and file systems with diagrams.
- Use Linux regularly to see OS ideas in action.
Operating Systems: Frequently Asked Questions
What is virtual memory?
Virtual memory lets a system run programs larger than physical memory by using disk space as an extension of RAM.
What is thrashing?
Thrashing occurs when a system spends more time swapping pages than executing, because there are too few frames available.