Introduction

What is an OS?

OS- An interface between computer hardware and the user

What happens if there is no OS?

If user wants to access the devices on the PCB, user would have to write a program to access the device

What are the functionalities of an OS?

1. Resource Manager If a number of users are trying to access some hardware/device, we need a resource manager to allocate and de-allocate resources continuously (esp. in parallel processing)
2. Process Management CPU scheduling - executing multiple processes at the same time (eg chrome, vs code, spotify)
3. Storage Management How to store data on a system - stores through filesystem - how to store permanently
4. Memory Management Limited memory - processes which need to execute come to the RAM before going to the CPU - allocation and de-allocation from RAM continuously
5. Security Blocking cross process data access - security in the form of authentication - permissions (sudo)

What are the various types of Operating Systems?

1. Batch OS - batch of similar kind of jobs given to CPU to be computed - data/jobs loaded on punch cards - go to the system - give to operator - operator makes a batch of jobs - get results - CPU does not go the next job unless first job is completed (non-pre-emptive)
2. Multiprogramming OS -
   • We bring multiple processes into the RAM - as many as we can
   • Non pre-emptive execution (scheduling)
   • For eg - if P1 goes to CPU - CPU will try to execute P1 completely unless P1 wants IO. In that case, CPU sends P1 to IO manager and brings in another process P2 for execution.
   • Focus on decreasing idleness
3. Multitasking OS (timesharing) -
   • Pre-emptive scheduling
   • Fixed time slots for each process, regardless of whether all instructions are complete or not
   • Improves response time (more responsive)
4. Real Time OS -
   • Real time environment, cannot afford delays
   • Hard - No delay can be bared at any cost (eg missile launch)
   • Soft - No critical situation so we can afford a little bit of delay (eg. YT live)
5. Distributed OS -
   • Geographically separated machines
   • Connected via a network
   • Loosely couple environment
   • Improves availability, fault tolerance, scalability
6. Clustered OS -
   • Different machines connected via a local network
   • Improves computation power
   • Improves availability, fault tolerance, scalability
7. Embedded Systems -
   • Works on fixed functionality
   • Cannot be changed, can only handle whatever was programmed into it and stored on the circuit board
   • eg washing machines, oven, AC

Processes