GATE CS 1996 Q1.20 — I/O Scheduling

SPOOL stands for Simultaneous Peripheral Operations On-Line. It is a technique used to temporarily store data in a buffer (usually on a disk) so that a slow, non-shareable input/output device can access it at its own pace without blocking the faster CPU or other processes.

Let's analyze the options:

• Option A (A line printer): A printer is a classic example of a spooled device. Since a printer is slow and cannot print pages from multiple jobs simultaneously (which would interleave and ruin the outputs), the operating system intercepts the print commands and writes the output data to a spool file on the disk. The printer then processes these jobs sequentially from the queue.
• Option B (A terminal): Interactive terminals require real-time, direct communication with the running program rather than delayed spooling.
• Option C (Secondary storage in virtual memory): This involves paging or swapping mechanisms, which manage memory allocation rather than spooling I/O operations.
• Option D (A graphic display device): Graphic displays render output in real-time directly to the screen for user interaction.

Therefore, a line printer is a standard example of a spooled device.