Spooler

The spooler is the central coordinating process for the print subsystem. It gives the user flexibility in organizing and optimizing the use of the system's printers. The spooler has a global view of the system's printing resources, particularly in a server environment and therefore is able to make the best use of those resources.

• The spooler ensures that print output from two separately executing applications cannot be intermixed on the printer. As an optional optimization, the spooler can start a printing job before it is completely queued. Any successive jobs are queued normally.

• The spooler can print a job in the background while the user continues to use the application. Other single-tasking operating systems, such as DOS, require the user to wait until the print output is sent completely to the printer.

• The spooler can send jobs from PM applications across a network to a remote server, without the application's knowledge.

  Note: The file system handles print jobs from non-PM applications.

• Queues within the spooler can be used for various purposes. For example, one queue could be used for large print jobs that are printed at times when print demand is low. Another queue could be configured to print jobs using a special size paper. Print jobs on this queue would be held until the correct paper is loaded into the printer.

• The spooler can support a number of printers simultaneously. It can be configured so that jobs on a single queue can be shared among all the printers. This load balancing, which is particularly important in server environments, can be achieved without the application's knowledge.

• Jobs can be prioritized while in the queue. For example, an urgent job can be given a higher priority than ordinary jobs.

The spooler consists of one or more print queues, one for each printer object defined by the user. Jobs are created by applications and placed in a queue, waiting to print. When the previous job is completed, the next job in the queue is sent to the printer.