Windows NT printer drivers, which run in “kernel mode”, introduce a high risk for the stability of the system if the driver is not really stable and well-tested. And there are a lot of bad drivers out there! Especially notorious is the example of the PCL printer driver that had an additional sound module running to notify users via soundcard of their finished jobs. Do I need to say that this one was also reliably causing “blue screens of death” on a regular basis?

PostScript drivers are generally well-tested. They are not known to cause any problems, even though they also run in kernel mode. This might be because until now there have been only two different PostScript drivers: the one from Adobe and the one from Microsoft. Both are well-tested and are as stable as you can imagine on Windows. The CUPS driver is derived from the Microsoft one.