## Virtual Device Driver Reference for OS/2

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### Printer Close Processing

BIOS printer interrupts operate on a single-character basis, which can have a negative impact on printer and system performance. For this reason, the VLPT buffers BIOS print requests. When the buffer becomes full, print requests are sent to the file system to be spooled and printed. The size of the application's print request is rarely an even multiple of the VLPT buffer size. This causes the virtual device driver to provide methods of flushing the remaining characters in its buffer.

A virtual parallel port device driver's BIOS INT 17h buffers are flushed in one of four ways:

DOS settings PRINT_TIMEOUT automatic close feature
Ctrl+Alt+Print Screen key sequence (VDHPrintClose)
Application termination
DOS session termination