Frankly, to a lot of folks, it doesn't matter: A lot of people run standalone machines because of malware fears. Sure, the malware eats some CPU cycles, but that's more than offset by not needing A/V and a firewall. Even the network connection itself uses considerable resources.

Sierra(Kings Quest, Space Quest, Larry) used to require you to enter a word from a randomly selected part of the manual to play the game, otherwise it would instantly flag you as having lost.

There also used to be a game that used a kind of optic lens to decypher a page of encoded passwords that was used as DRM by someone. For some reason that never caught on and developers instead moved onto burning untransferable verification codes onto the CD.

For a while, UBISoft used to have a very intrusive verification mechanism that was based on that principle. I think they used those untransferable codes to encrypt the actual program or something. Most notorious for its use in the Silent Hunter series.

In a way, mandatory clients are a step up from that, but i still don't like it. Makes me feel like i got to call Coca Cola, or one of their bottling companies every time i want to pour out a glass of soda instead of that permission being implied by the fact that i bought the soda from a grochery store (and before you bring up the point of buying a license to use instead of ownership, soda bottlers tend to declare that they continue to own deposit bottles even after you buy them, so you do effectively buy a license to use the bottle).

I tolerate Steam because it is relatively non intrusive, i already got an account there and they got good deal ocasionally. I won't get a UPlay or Origin account though. I keep hearing horror stories about the performance drain UPlay inflicts, and EA still doesn't appear to have grasped the concept of selling online titles for cheaper than the retail box (or decreasing the sales price of a title as it gets older for that matter seeing as i often see 3 year old EA title STILL sell for 40 to 50 EUR, which i consider the top price for a brand new AAA title).

"My definition of DRM is..." means DRM that "you" don't like.
DRM has one reason to exist, which is to prevent a product being used without paying the creator(s) first. It has many different formats and the actual ability to prevent unauthorized use is irrelevant.
Unauthorized use requires another copy of the product, so all DRM is copy protection and vice versa.
Whatever the actual method any specific type of DRM is using, how effective it is at stopping unauthorized use and whether you can put up with that method, makes absolutely no difference to the definition.

The core fact is DRM is all forms of copy protection.

This is not "My definition", it is defined by the intended purpose of all forms of DRM.

To use an unauthorized copy always requires the existence of an unauthorized copy. This is what DRM is intended to stop. It's one and only purpose.

It is that purpose that defines it, not anyone's preference.

What about multi-computer licenses? I can install Steam games on multiple computers, and it's not necessarily unauthorized use. Family Sharing is authorized use that requires another copy of the product as well.

How does that work with DRM'd games?

DRM can be used as copy protection, and Copy Protection can be used as DRM, same way as a bed can be used as a table, and a table can be used as a bed. But a table isn't a bed, nor is a bed a table.

I'm not crazy about your take on it, but I guess it's valid too.

Copying a game is not theft. DRM doesn't prevent copying, it makes it a bit less convenient and is used to gain control on the consumer.

DRM is just that the publisher enforces on you, how and when to use his product.

On GOG, all that is left: the redistribution, reverse engineering and alteration of the software, which is not allowed.

When B&W2 was released, I bought it and immediately hated it, because it wouldn't run but instead told me to uninstall my daemon tools. At that time I already used to make digital copies of my cds and mount them instead of putting them in and out the CD-Rom all the time.

It doesn't always have to be a closed environment like Steam to enforce DRM.

RA3, was a nightmare. I bought it (pre-ordered as dvd) from EA and was only able to play it for ~2 weeks, because I reinstalled it too often. Then they removed the DRM in a patch, so I had to install and patch the DRM away to be able to play, but the installation from my DVD wouldn't accept my key any more. I loved the whole C&C series and hated RA3 because of this, never really played it afterwards.

You said that it requires a copy, not an authorized copy, and that DRM prevents copying.

Copy Protection regulates distribution, DRM regulates execution. Being unable to copy a DVD does not prevent running a game without the DVD, and requiring a DVD does not mean you can't the DVD.

And what about software that requires hardware dongles to run? You can copy the software as many times as you want, but can only run it if you have the dongle. The DRM is on all the copies, though the dongle is only in one. And I can use my dongle with your copy of the software, without installing a copy of mine.

Another question. CD-Key that is required for installing, but doesn't matter for playing. Kinda like Win95 serials.
Is that DRM or Copy Protection? Or both, even though only half of the requirements are met?

If you think of DRM as a more active component with code (as in checks are done each time you run it) then i'm not sure. Win95 might not check the serial on each startup, but later versions of windows do. And while installing the software if you didn't have easy access to a key (for some reason) then it would definitely be DRM for the duration since you can't use the computer until you have a good key (but i know you could copy the install files locally before starting... removing the need for a CD driver).

Windows activation process.
Check for SLIC certificate in Windows. If exists, check for corresponding SLIC certificate in BIOS. If exists, Windows is activated.
If any of the above is false, then it moves to serial check. The check is offline as well, after the initial activation (online or offline), with updates being able to modify the list of valid serials.
Unsure if KMS activation requires unique serial or only allows up to X machines active with the same one. Haven't really followed the Enterprise line

Are we still talking about Windows? You can install Windows without a serial, though it will be the trial version. So full access for limited time.

Assuming DRM is somhow not copy protection and copy protection is stopping all copying completely, because that's the most common form of copy protection, is not accurate. All exceptions are authorised copying, which is not the intended to be stopped by DRM, though much of the time lazy publishers take that easy route.
DRM's intent as opposed to it's result, is the only legitimate definition it can have, that intent is to stop unauthorized copying, The fact it is usually done by stopping all copying does not change the intent, all exceptions are attempts to allow legitimate copies while stopping the stolen ones.
DRM is always copy protection because a stolen product is a copied product, it is an attempt to stop the, theft through copying the product.
I know discs and serial keys can also be stolen, but that's not the subject here and DRM can't stop that at all.

The success or failure of DRM in achieving the desired aim of preventing theft by copying doesn't make any difference to that being the aim.

The sole intended purpose is to stop theft by copying. That never changes, therefore by definiton of purpose:

DRM is Copy Protection

Protection does not mean stopping all copying, just unauthorized copying.
Steam is a form that additionally tries to stop multi-installs as well by not even providing an installer, which is usually what is actually copied by the way, rarely is the game itself copied.

Maybe you can find an exception to this general rule, all generalizations usually have exceptions, which is why the expression;
"The exception proves the rule"
is always used. Not because the exception actually proves the rule, of course it doesn't, it is said because it is just as untrue to think an exception disproves a rule.
Trying to find exceptions to prove this general rule is wrong just doesn't work. It never does.

I'm pretty much on board with this. A CD key doesn't bother me too much. How I measure DRM is this:

One of my computers is not connected to the internet in any way. If I can install and play a game on that machine without having to connect to the internet, then the game does not have DRM. If I can't do that, then the game has DRM.

Of course, there are mild forms and more evil forms of DRM, some forms of which I'm willing to tolerate, but the above is what I use to define whether a game has any sort of DRM or not.

Unauthorized usage. Not copying. I can install my steam games on a friend's computer, but he won't be able to play them. I can copy the Securom games to other computers, but they won't be able to play them. I could (back in the Win2K era) install Windows on 2 different PCs using the same serial, and only problem would be if they were both online at the same time.
DRM is not to stop unauthorized copying. It's to stop unauthorized usage.

P.S. All UPlay games can be installed without owning a license for them. To play them, you need a license. So the UPlay DRM allows you to make as many copies of the game as you want, but only allows you to play if you own the game. Or is that "authorized copies" as well?

Steam actually allows multiple installs quite easily. It doesn't allow multiple uses though.

P.P.S. The point I'm trying to make is the point already made in this thread (and others) multiple times. DRM is something subjective. CD-checks may or may not be DRM. Serials may or may not be DRM. One time activation may or may not be DRM. Lack of an installer may or may not be DRM.
Claiming that "DRM is X and only X" is at best shortsighted, at worst moronic.

Translation: Big pain in the ass and DRM...

Honestly once this computer dies I'm probably never using windows again, same with consoles, I've given up on them and once those die I'll do PC gaming exclusively..