(Simultaneous Peripheral Operations OnLine) The overlapping of low-speed operations with normal processing. Spooling originated with mainframes in order to optimize slow operations such as reading cards and printing. Card input was read onto disk and printer output was stored on disk. In that way, the business data processing was performed at high speed, receiving input from disk and sending output to disk. Subsequently, spooling is used to buffer data for the printer as well as remote batch terminals. See print spooler.