long-term scheduling

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1. What is a long-term scheduling? How it is differ from short-term scheduling?

A process migrates between the various scheduling queues through out its lifetime. The operating system must select for scheduling purposes, processes from these queues in some fashion. The selection process is carried out by the appropriate scheduler.
In a batch system, often more processes are submitted that can be executed immediately. These processes are spooled to a mass storage device, where they are kept.

Long-term scheduler
The long term scheduler or job scheduler selects processes from this spool and loads them in to memory for execution.
The long-term scheduler decides which jobs or processes are to be admitted to the ready queue; that is, when an attempt is made to execute a program, its admission to the set of currently executing processes is either authorized or delayed by the long-term scheduler.
Long-term scheduling is also important in large-scale systems such as batch processing systems, computer clusters, supercomputers and render farms. In these cases, special purpose job scheduler software is typically used to assist these functions, in addition to any underlying admission scheduling support in the operating system.