As you have read before, DVD Regions play an important (albeit annoying) role in the DVD world. Most drives up to the 3rd generation support what is called RPC-1. This simply means that the DVD-ROM drives do not play a part in controlling the playback region. It is solely dependent on the decoder. Later drives, like the Pioneer 114 (10X) or newer are factory set to RPC-2 (due to the persistent nagging of the DVD Forum). This is bad because the region control now relies on the DVD-ROM drive's hardware, which is hard to "hack". You'll usually get a counter, usually 5, which counts down every time you play a different regioned disc. So when it counts down to nothing, your drive will be automatically locked in whatever region it is in last - and it can't be reversed !! Older Pioneer drives also had the RPC-2 option, but you had to physically remove a jumper on the drive for it to be set (so be warned, if you have a Pioneer drive, don't play around with the jumpers). Most well known brands of drives today can be changed from being RPC-2 to RPC-1 with a "hacked" firmware update - for more information, please refer to DVD Digest's Complete Region-Free DVD Guide.
If you've had a look around the vast number of DVD-ROM drives available, you might notice that the some drives lack the "SPDIF" socket. You may also hear alot being said about the wonders of this "SPDIF" socket, allowing you to connect to an external Dolby Digital reciever to decode DVD soundtracks. Well, both are right. BUT, the SPDIF socket on the DVD-ROM drives has nothing to do with the Dolby Digital sound stream, and its transmission. Dolby Digital sound streams travel through the PCI bus to reach the decoder (or your soundcard) and the SPDIF socket on your DVD-ROM drive is not needed for this operation. The SPDIF socket your DVD-ROM drive is used for the transmission of digital audio from music CDs only, it has no other use. In fact, my old Panasonic 2X CD-ROM drive has this socket, and I've never had to use it.