An example of true CUPS drivers are the Gutenprint drivers included with a customized installation of Snow Leopard. There are still a number of Canon files that are installed by the driver so that you can perform certain functions that are typically not available to CUPS drivers, such as printing on CD's. Note that the reason I say so-called is that Canon does not appear to have completely stuck with using the core files of CUPS for printing. If you use a driver that has Carbon-based plugins, such as the print dialog extensions (PDEs) and you are using a 64bit application, such as TextEdit, then the PDE's will be shown with a line through them, meaning they are not compatible. With 10.6 moving to a 64bit system, the vendors needed to write the drivers using the newer code so that they were more compatible with the new platform. The non-cups drivers, such as those used in 10.5 and earlier, have plugins and filters written in Carbon, which is an older language. The so-called Canon CUPS driver uses plugins and filters written in Cocoa and are meant to closely interact with the core printing system in OS X, known as CUPS (Common UNIX Printing System).