You're right jlliagre. DMA registers are 32-bits too. That was my fault. I tought about the possibility that the kernel addresses +32bits without a PAE-like feature and without DMA instructions when accessing large ranges. Kind of Large File Support in 32-bit systems.

Windows is a strange operating system. It supports
http://www.microsoft.com/whdc/system...AE/PAEdrv.mspx

After reading that, I'm not convinced a Windows process can address more than 4 GB (and perhaps more than 3 GB) when PAE is activated, at least at a single time. This looks more a device driver thing.

It reminds me too the old 16/32 bit CPUs segment registers, with their near and far pointers nightmare ...