Digital Rights Management (DRM)
DRM associated with accounts is weaker than most but still present, requiring online activation via CD key to access online services such as multiplayer and profile stats. These games require you to activate the game through their servers and use their accounts to activate the game, and many require these accounts to access the game. For single-player games, account-based DRM often does not affect the game to any real degree, as you can play them with an offline profile without activation. Because of this, many consider single-player account-based DRM to not be DRM at all because it does not require any contact beyond having the packages installed; no Internet connection is required. Games falling into this “single-player only” category will be marked as such.
EA Accounts exist for two purposes:
To activate and run the game. This requires a constant Internet connection, even in single-player modes. The benefit to this, however, is that DLC, if it exists, is more easily managed than below.
To access online features, including DLC. In this case, the EA account is not required to access single-player (in some cases, it may be required to activate the game). For DLC, however, the game will require an account either way.
This list will be categorized as such, as well as games that use EA Classic accounts. Single-player games in the latter category will be specially marked, either as an option or exclusively single-player.
Stardock distributed their games via Impulse. After they sold it to GameStop in March 2011, Stardock introduced account system for their games to distribute patches and for the official support on forums. Their older games are de facto DRM free after registration, and those games are noted. You can download them any time from your Stardock account. In 2012, Stardock switched to Steamworks because of multiplayer. Those games can't be downloaded from Stardock, only from Steam.
Hardware-based DRM uses components of the PC such as the MAC address of network adapter(s) and serial number(s) of hard drive(s) to create a hash or signature which is used for identification of the PC in the DRM activation process. When a game which incorporates this type of DRM is run, it checks that the current components of the PC match the hash/signature which was created and stored during the previously completed activation. The tolerance for matching this hash varies by game, but in general if a significant component or components of the PC which comprise the hash have changed, the DRM will require a new activation to play the game. If an activation limit exists and is reached, the game will refuse to play. In most cases where this type of DRM is used, there will be methods to either revoke activations or reset the limit so a new activation is performed. These will be noted at the bottom of their respective sections below.
... further results
Some games on Steam contain remnants of DRM that has been removed (e.g. S.T.A.L.K.E.R.: Clear Sky or Dead Space) or DRM files which are not used unless you attach a DRM expansion pack or DLC to the game. The DRM files do nothing, install nothing and are completely inert unless otherwise noted.