Artigo da Microsoft Ocorre 100 por cento de uso da CPU quando você imprime em uma porta de impressora LPT diz:
SYMPTOMS
When you print on an LPT printer port, 100 percent CPU usage occurs until the print job is completed. This slows down other programs until the print job is completed. In some case, other programs may slow down enough that they seem completely unresponsive. This behavior affects all power users who have many programs running at one time.
CAUSE
This behavior occurs because Windows does not have interrupt support for LPT printers.
WORKAROUND
To work around this behavior, print to a Universal Serial Bus (USB) printer port. If the printer does not have this capability, use a parallel-USB cable.