Black Box Explains... Buffers.
A buffer (also called a spooler or a cache) is a temporary storage device used to share printers and compensate for a difference in speed and data flow between two devices. Buffers use RAM (Random-Access Memory) to take in data and hold it until the receiving device handles it.
A buffer serving a computer can be installed either internally or externally. Internal computer buffers are common in the forms of keyboard inputs, data caches, and video memory. An external buffer is usually used for printing.
An external buffer downloads jobs to the printer, freeing the computer so you can get back to work sooner.
A print buffers ports can be serial, parallel, or serial and parallel. Because a buffers ports operate independently of each other, a buffer also can be made to perform serial-to-parallel or parallel-to-serial conversion or to change the word structure and/or serial data rate (baud rate) of the data.
While most buffers are FIFO (First In, First Out), some advanced units can function as random-access buffers. For most serial buffers, hardware flow control is required, but some also support software (X-ON/X-OFF) control. Most buffers support printing of multiple copies of a document, provided the buffer has enough memory to store the entire print job.