(simultaneous peripheral operations online) is it all about?
It is a kind of buffering mechanism or a process in which data is temporarily held to be used and executed by a device, program, or system. Data is sent to and stored in memory or other volatile storage until the program or computer requests it for execution.
Why the need for spooling?
Because our CPU performs very fast execution about 2.3Ghz.So CPU waits much time receive the next I/O. Because of printers and punch card readers etc (batch processing), are very slow relative to the performance of the rest of the system. Getting input and output from the system was quickly seen to be a bottleneck.
Spooling works like a typical request queue where data, instructions, and processes from multiple sources are accumulated for execution later on. The spool is processed in a FIFO manner i.e. whatever first instruction is there in the queue will be popped and executed.
Applications/Implementations of Spool:
A batch processing system uses spooling to maintain a queue of ready-to-run jobs which can be started as soon as the system has the resources to process them.
Spooling is capable of overlapping I/O operation for one job with processor operations for another job. i.e. multiple processes can write documents to a print queue without waiting and resume with their work.
E-mail: an email is delivered by an MTA (Mail Transfer Agent) to a temporary storage area where it waits to be picked up by the MA (Mail User Agent).
The most common can be found in I/O devices like keyboard printers and mouse. For example, In a printer, the documents/files that are sent to the printer are first stored in the memory or the printer spooler. Once the printer is ready, it fetches the data from the spool and prints it.
