The print jobs held in a spooler queue are known as spool files. Spool files contain the following:
Print job data is in one of two formats:
Standard output data, PM_Q_STD is spooled as a PM metafile; that is, as a series of graphics orders stored in a packed binary format. PM_Q_STD print jobs are created through the GPI.
An advantage of the PM_Q_STD format is that the files are smaller than PM_Q_RAW format files. The smaller size saves disk space for jobs in the spooler queue and reduces network traffic when transmitting the data to a network server.
The content of PM_Q_STD jobs can be viewed using the PICVIEW application. This is achieved using the job-content menu on a print job in the printer object. The multi-page spool file can be shown in a device-independent manner so that the content of the job can be recognized easily.
After a job is spooled and ready to print, the spooler sends the PM_Q_STD job to the queue driver. The queue driver replays the metafile, through the GPI, to the appropriate printer driver. The driver, in turn, converts the data to printer-specific commands, that is, a printer-specific format.
There are some restrictions on the content of PM_Q_STD jobs that are related to the restrictions for PM metafiles. PM applications that cannot deal with these restrictions should enqueue print jobs using PM_Q_RAW, but there is an increase in required disk space and, possibly, network traffic.
Print jobs sent to network servers that do not support PM are converted automatically to the PM_Q_RAW format by the system. The application still can continue specifying PM_Q_STD.
Note: The effect of converting all PM_Q_STD print jobs to PM_Q_RAW can be turned on by the user's selecting Printer-specific format in a printer object settings page.
Raw data, PM_Q_RAW, is the actual printer command to print the job. For example, raw data created for an HP** LaserJet** printer contains Printer Command Language (PCL) commands; and raw data created for a PostScript** printer contains PostScript commands.
The content of PM_Q_RAW jobs can be viewed with the system editor. This is achieved using the job content menu on a print job in the printer object. However, it is not always easy to recognize the content of a job. For example, PostScript is very hard to understand and get a visual idea of the actual output.
Print jobs are created by the file system as a result of printing directly to the physical port using either INT 17 or INT 21 under DOS or the OS/2 DosOpen API. These print jobs always are queued using PM_Q_RAW. The actual queue chosen depends on the port used and the configuration of the print subsystem.
PM applications also can use the PM_Q_RAW format, but the overall print-job creation process normally is slower because the printer driver has to perform more work to create the printer-specific format.
If the Print while spooling printer object setting is turned on, the user can perceive a faster response. In particular for a multi-page document, the first page starts printing as soon as the printer driver has completely finished converting the GPI to the printer-specific format.
Note: PM applications always should specify the PM_Q_STD format. The difference in disk space used can be from a factor of 2 to a factor of 50. The Printer-specific format and Print while spooling printer object settings can be used to configure optimal performance for the environment.
Although the base operating system supports the two print job formats described above, other formats can be supported by providing an appropriate queue driver.