1) Batch OS-:

• Here, the jobs are executed in batches.
• The system puts all the jobs in a job queue. A specific portion of the job queue is loaded with OS.
• The selection criteria used by CPU are FCFS.
• The users collect their respective output when all the jobs get executed.

     Disadvantages-

• Starvation -In the above figure, let’s assume there are 4 jobs. If the 1st job takes 100s for its execution. For this much amount of time, all the remaining processes will have to wait or they will never be executed. This is termed as starvation.

2) Multiprogramming OS-

• Multiprogramming is an extension to batch OS.
• Here,CPU is always kept busy.
• If there is a process waiting for some I/O operation, then the new process can be loaded into CPU.

    Advantages-:

• overall efficiency and throughput of the system is increased

3)Multiprocessing OS-:

• In the Multiprocessing, Parallel computing is achieved.
• Here, we have more than one processor and each processor is given a job.
• The execution of jobs takes place in parallel.

4)RTOS(Real-time OS)-:

• In Real-Time Systems, each job carries a certain deadline within which the Job is supposed to be completed. Application of a Real-Time system exists in the case of military applications, if you want to drop a missile then the missile is supposed to be dropped with a certain precision.

You can refer to this YouTube video for Video Explanations