Buffers & Spoolers J L Martin 2009

Think about it… All I/O is relatively slow. For most of us, input by typing is painfully slow. From the CPUs point of view, even very fast typists are so slow that theyre hardly doing anything at all! Screens and printers work a fair bit faster than a typist, but all the same, the I/O system needs to work the devices efficiently so as not to waste the CPU.

Buffers A buffer is an area of memory (RAM) used to temporarily store data when it is being transferred between a computer and a peripheral device. A buffer is an essential part of an interface between parts of the computer system that work at different speeds. A printer buffer can receive data at a much higher speed than the printer can print, thus freeing the computer from the print job Fast computer Slow(er) printer Large print job

Spoolers When large amounts of data are to be sent to a peripheral device, or when the peripheral is shared across a network then spooling is a preferred method of compensating for the difference in speeds of the processor and the peripheral. Spooling involves the input or output of data to a tape or a disk. This, for example, allows output to be queued from many different programs and sent to a printer by a print spooler (special operating system software). The print spooler stores the data in files and sends it to the printer when it is ready, using a print queue.

Background printing Fast backing storage such as a hard disk is used for the temporary storage of printing jobs. The data is held on disk and transferred to the printer at a speed which the printer can accept. This is called background printing because the user can continue working on a different task such as keying in. This is called the foreground task because in between key presses, the CPU will handle the print job. Printer server Print jobs are spooled on printer servers hard disk

Advantages and Disadvantages One advantage of a printer spooler over a buffer is that a buffer has a fixed size (usually Mb) whereas the spooler is using the hard disk which has a much larger size (usually Gb) So if your print job is larger than the buffer, your computers CPU will not be entirely free of the print job. A disadvantage of spooling might be if you are running out of space on the hard disk!

Copy Buffer –Area of temporary memory used to store data being transferred between a computer and a peripheral device. –Usually part of peripheral device (e.g. printer) –Fixed size Spooler –Uses an area of the computers hard disk to do the same job.