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Which of the following is an example of spooled device?

  1. A line printer used to print the output of a number of jobs
  2. A terminal used to enter input data to a running program

  3. A secondary storage device in a virtual memory system

  4. A graphic display device

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Answer is (A).

Spooling(simultaneous peripheral operations online) is a technique in which an intermediate device such as disk is interposed between process and low speed i/o device. For ex. in printer if a process attempt to print a document but printer is busy printing another document, the process, instead of waiting for printer to become available,write its output to disk. When the printer become available the data on disk is printed. Spooling allows process to request operation from peripheral device without requiring that the device be ready to service the request.

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Spool Device

Spool Device is a buffer that is used to store/hold output for a device . Certain devices such as tape drives and printers are incapable of multiplexing different I/O requests from different applications at the same time . The OS performs the operation by simply using spooling process which is handled by in-kernel thread or system daemon process , since printers can only service one request at a time so by using spooling process the different requests (output from the application ) are spooled to a disk file which are later queued and transferred to the printer one at a time.

 

(A) is the correct answer as Printer cannot accept interleaved data-streams , it needs spooling to service multiple requests .

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Correct Answer is (A)

In operating systems, a spooled device refers to a device (such as a printer) that utilizes a spooling (Simultaneous Peripheral Operations On-line) technique for handling input/output operations.

When a spooled device is used, data to be printed or processed is first stored in a buffer or a spool file on the system's disk or in memory. This allows the system to handle multiple requests concurrently without having to wait for the device to become available. The spooling system then manages the process of transferring data from the spool file to the device, allowing the application to continue its operation without waiting for the device to finish processing.

Spooling helps improve system performance and efficiency by decoupling the device operation from the application, reducing idle time, and enabling multiple tasks to use the same device simultaneously. It is commonly used for printers, where multiple users may submit print jobs simultaneously, and the spooler manages the print queue and schedules jobs for printing.
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