Long Term Scheduler in Operating System

Pre-requisites: Process Schedulers in Operating System

A long-term scheduler, also known as a job scheduler, is an operating system component that determines which processes should be admitted to the system and when. It is used in batch processing systems and operates at a high level. The long-term scheduler is in charge of allocating resources such as processor time and memory to processes based on their needs and priorities. It also determines the order in which processes are executed and manages the execution of processes that may take a long time to complete, such as batch jobs or background tasks. Because it operates at a higher level and does not need to make scheduling decisions in real-time, the long-term scheduler is typically slower to respond than other types of schedulers, such as the short-term scheduler. However, it is an essential component of the operating system because it ensures that the system is used efficiently and effectively.

Functions of Long-Term Scheduler

• Long-term schedulers are in charge of determining the order in which processes are executed and managing the execution of processes that may take a long time to complete, such as batch jobs or background tasks.
• A long-term scheduler’s primary function is to minimize processing time by taking the mixtures of CPU-bound jobs and I/O-bound jobs. 
  • CPU Bound Jobs: CPU-bound jobs are tasks or processes that necessitate a significant amount of CPU processing time and resources (Central Processing Unit). These jobs can put a significant strain on the CPU, affecting system performance and responsiveness.
  • I/O Bound Jobs: I/O bound jobs are tasks or processes that necessitate a large number of input/output (I/O) operations, such as reading and writing to discs or networks. These jobs are less dependent on the CPU and can put a greater strain on the system’s I/O subsystem.

Limitations

• Response time: Because long-term schedulers operate at a higher level and do not need to make scheduling decisions in real-time, they are typically slower to respond than other types of schedulers, such as short-term schedulers. This may result in longer wait times for processes awaiting admission to the system.
• Accuracy: Because they do not have real-time data on the state of the system, long-term schedulers may be limited in their ability to accurately predict the resource requirements of processes. This can lead to inefficient resource allocation and poor system performance.
• Flexibility: Because they operate at a high level and are not designed to handle real-time or interactive workloads, long-term schedulers are typically less flexible than other types of schedulers. This can make it difficult for them to adapt to changing workloads or system conditions.
• Overhead: Long-term schedulers can introduce overhead because they require more time and resources to evaluate and manage process execution.

For more details please refer Difference between Long-Term and Medium-Term Scheduler article.