What is "no-intro"?

We are a group of people that loves to catalog games. More information on the home page.

What is "dat-o-matic"?

It is our database, where you can browse our catalog and download .DAT files.
There are no ROMS online.

What are "headers"?

Back when NES and Lynx ROM images were first being dumped, the emphasis was not as much on preversation as it was people just wanting to share and play the games. People didn't think about the consequences of headers back then and how they would later affect game preservation. A set number of bytes, known as headers, were written to the tops of all NES and Lynx ROM images. These headers are not part of the original game's data, and are only present to tell emulators how to properly run a ROM image. Although emulators should handle that sort of data on their end, (N64 emulators do, anyway) NES and Lynx emulators don't, instead requiring those headers on top to this day. Hopefully in the future things will change (Nestopia has made some progress for NES ROM images), but for now those headers are required.

What are the differences between the "standard dat" and the "P/C XML"?

The standard dat is just that. It's all of the known ROM images and BIOS images put into one dat with no sorting. The P/Clone dat, however, groups games together if they are very similar. For example, in the SNES P/Clone dat the USA game Secret of Mana is grouped with the Japanese game Seiken Densetsu 2. If you played them both or seen pictures/video, you would see that they are almost entirely the same game, with the primary difference being their languages. Some of these games have altered graphics and sound between regions, such as the NES games Castlevania III - Dracula's Curse (USA) and Akumajou Densetsu (Japan). They are similar enough to be grouped together in the dat. Sequels, even if they are similar to their predecessors, are counted in their own group, of course.
In a P/Clone dat, you can instruct your ROM manager to delete "clones" if you desire. Just tell it which region you prefer to be the carrier of the title of "main" AKA "parent", and it will assign all others in the groups as "clones". You may also be able to assign a second most preferred region, a third, and so on. If you were to assign, say, USA as the "parent" region, then all non-USA games would be assigned as the "clones" as long as there are USA games in their groups. If there are not, then your second-most preferred region is to be considered the "parent" in that group and so on down the line. Some groups will only contain a single ROM image, and if so then that image is instantly the parent of its group.