Definition: Spool

What is Spool?

Simultaneous peripheral operations on-line or spool is a parallel way of executing tasks between I/O devices by using secondary storage as a buffer where instructions are stored/queued until they are called for execution.

Why do we need it?

I/O devices operate at a significantly slower pace than CPU. Due to this mismatch of speed, we needed a protocol to simultaneously and effectively process data, take inputs, and give outputs. This is where spool comes into play.

How does it work?

The typical spooling protocol makes use of secondary storage in the CPU or buffer in I/O devices, for example, a printer buffer.

• First, the input data is stored in the secondary storage.
• Later, CPU loads the data into its main memory, processes it, and stores it back in the secondary storage.
• Lastly, the output device outputs the data stored/queued in the secondary storage.