I'm pretty new to PC games. I've only been buying PC games for about 10 months and have been buying the classics fom GOG for about three months now. I've read about DRM on Wiki, but I would like a simple breakdown of this. I have used GOG, Steam, d2d, and Impulse to buy games. How do these different sites handle this? Do I actually own these games? What sites are better than others? What happens if one of these sites go under? Any help will be appreciated.

GOG: No DRM, you "own" the game in that the file you download is yours to do with as you please forever (provided you don't delete it or otherwise lose it). GOG does allow you to re-download all your purchased games as many times as you want. If GOG goes under, you can still use your games.
Steam: The client is DRM in and of itself, in that it is required to validate, decrypt, install and run the games. While you do have the freedom to install (most) games bought through the client on as many computers as you want, you can have the access to those games revoked for violating any of Valve/Steam's rules. If Steam goes under, you could lose access to all your games, but they have stated in the past that they would not let that happen
D2D: DRM really depends on the game. Most require some kind of online activation, but others are virtually free of DRM completely. AFAIK, you are only given a limited amount of time to download your files and once that time is up, you can never get them again without purchasing an additional "extended download service". If D2D goes under, you might lose the ability to re-install your games, but games that are already installed will continue to function.
Impulse: Pretty much a hybrid of Steam and D2D. DRM usage depends on the game, and the Impulse client is not required to run any of the games, but it might be required to obtain updates for the games. If Impulse goes under... it depends on the game. Any that required some kind of activation might not be re-installable, others might have no issues at all.
With all digital services, you don't actually own anything, you are only licensing the use of the software. Some like GOG don't have the ability to remove your access to the software, so you do in effect "own" the game. Others like Steam are more like a rental service, in that your access to the games is completely under Valve's control.
As for which ones are better than the others, it all depends on what you are willing to accept. If you want full control of the games you have purchased, then GOG and selected titles from D2D or Impulse are the best. If you just care about the games, then whichever one has the best games at the best price is the best. Its really up to you.

Thank you for for explaining that. I think I might buy more box games. I'm thinking digital distibution might not be as great as I thought. Hey, since you took the time, give me your email and a game and I'll hook you up.

Before you do that, you should know that games you buy retail can also have DRM. It's best to do research before you buy there as well.

I don't get that. I have the disk right? I can install whenever I like. How can DRM affect that?

Moreover, a few retail games tie their DRM to digital distribution (usually to Steam).

Some games require an internet connection to be made before you can install the game, which checks how many times you have installed the game against a preset limit and either enables or prevents you from installing the game.
Other DRM is a bit less intrusive, requiring you to enter in a CD key or have the disk in the drive to run.

Sometimes you have authenticate the game through the internet (and you get limited activation), and a few games may force you to use Steam (e.g. Empire: Total War). Some nasty DRM such as Starforce may even damage your DVD drive in long term.

Thanks anyway, but without the means for private messaging here, I won't share my e-mail addy with anyone.
Like PoSSeSSeDCoW mentioned, DRM is not unique to digital download services, it is also used in hard copy media. Some disk-installed games even require the use of Steam. If you are that concerned about it it, just make sure you research whatever title you are considering.
That being said, don't disregard digital distribution. Just as when CDs/DVDs replaced floppies, digital distribution is replacing disks. It might not happen tomorrow, but it is only a matter of time before disk-based installs of games will be a thing of the past.

Wow, I had no idea that was going on. That really ticks me off. I'm starting to understand why "DRM free" is such a big deal. Thanks.
Cow, he passed, you want the game?

Retail games can come with all sorts of DRM in them, such as Securom or Tages. It's a tool built into the game executable, even in some retail box games, that when they are run for the first time, they connect to their servers, authenticate, and take one activation away. They can also leave some nasty crap on your PC, trust me, I've had to deal with it before. While technically you can "install" the games as many times as you want, you'll run into trouble when you try to play the game. That's the part where it does the authentication. There are.... ways around it, of course, just like with any copy protection. But why should you even buy games that are DRM infected in the first place?
EDIT: You people reply too fast. Beat me to it!

I'd love it, thanks. For the game I'd like Incoming + Incoming Forces.
My e-mail is *redacted*. Thanks!
It's clarity is ambiguous. You have to know about it already to understand what they're talking about. It's definitely shady business on the part of publishers.
By the way, just got the game. Much obliged.

Actually, Demigod is in fact, one of the few games that is DRM free. Sure, you have to use Impulse to update the game, but I mean, you can totally install the game offline no problem, and even run the game without the disc in the drive. Hell, LAN works fine with one copy, and they even promote doing that.

Game sent. I'm starting to like GOG more and more. It was a little hard at first. I didn't grow up playing these games. I grew up on console games. I had to take a small step back. Sacrifice and Fallout 1 & 2 sucked me in though. I really like the way GOG works. Great prices, good service, great community.