Operating System
1. What is operating System
Operating system is the interface between the user and the hardware. This is the interface that help the user to use the applications, software and other information from the digital world.
Fig 1: Relation between operating system and user
2. Types of Operating System
1. Batch Operating System
Fig 2: Batch Operating System
According to the similarity in the jobs , the jobs are divided into batches and then these batches are processed by the Central Processing Unit. Suppose, three jobs arrived at the same time on the computer operator. The jobs are divided on the basis of their functioning as the same jobs in the one batch and then uploaded on the CPU to execute one batch at one time.
Advantage : Time saving as compared to mainframe as each batch containing one type jobs which are executed by its type of compiler.
Disadvantage : 1. Limited Memory
2. Less Throughput
3. Low CPU utilization
4. Low efficiency in terms of time, space, cost.
2. Spooling
Spooling term as Simultaneous Peripheral Operation Online. Pool means to store a huge amount of anything.
Fig 3: SpoolingInitially, when OS came into existence then we had to give the input to the CPU and CPU executes the instruction and finally gives us the output. But there was a problem with this approach , in normal situation, we have to deal with a number of processes and we know that the time taken in the input output operation is very large as compared to the time taken by CPU for the execution of instruction. So in the old approach, one process will give the input with the help of an input device and during this period the CPU is in idle state. Then CPU execute the instruction and at that time when it gives output the CPU again remain idle.
In spooling, the multiple input devices can upload the data on the disk and then main memory fetch the data from the disk to execute. At this time the CPU does not remain idle and when CPU is busy in performing some task the input device need not to wait to upload the data on the disk.
ADVANTAGE : 1. Need not to wait for CPU to free.
2. Input output operation overlapping is allowed in spooling.
DISADVANTAGES: It support only uni-programming.
3. Multi-programming Operating System
Fig 4: Multi-programming operating system
ADVANTAGE: 1. Context Switching
2. Response Time Decrease
DISADVANTAGE: 1. Waiting time
2. Job scheduling
3. Memory management is difficult.
4. Time Sharing or Multitasking or Multi-programming with round robin or Fair share
This approach is extension of multi-programming and uses one CPU. In multi-programming complete execution of job take place at a time while in multitasking the process execute in round robin fashion.
In multi - programming approach switching take place due to process but in multitasking switching is handled by CPU.
ADVANTAGE: Better response time.
DISADVANTAGE: Reliability is an issue.
5. Multiprocessing Operating System
The approach uses multiple CPU's
- Symmetric Multi-programming - No master slave, all processor have equal right.
- Asymmetric Multi-programming - Master-slave relation, one CPU controlling rest.
2. Graceful Degradation : Even when one processor fails rest are working and non stop computation is achieved.
3. Cost saving as only new processor needed rest circuit is same.
DISADVANTAGE: Throughput may decrease due to overhead or coupling.
6. Real-time Operating System
These are strictly bounded operating system.
Jobs must be completely executed within specified time otherwise system fails.
- Hard real time OS - No delay accepted in this type of OS. ex- Missile system satellite.
- Soft real time OS - Delay accepted. ex- Banking system, Live score.
