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We had some software delivered on a CD in which the vendor purposely put a defect on a specific track. If that defect wasn't there, the software could say it wasn't an original CD.

Since defects are not copied, even on low level track copies, an exact replica could not be created.

(preface: While Stephen's answer already covers the basic points, I would like to put a different emphasis here - and merge in some private history :))

Short answer:

It was the game's size and the need to copy it to a CD again, combined with expensive and unreliable writers. Further, the CD itself was used as a copy protection. While games often got installed completely onto HD, they did check every now and then if the CD was still present in a drive connected, so people could not install and run it on multiple (friends') systems.

All of this is based around the fact, that copying CDs was expensive and unreliable - at least until the early 2000s.

In general, it's a bit like it was with floppies in the very beginning (my fist 10-pack did cost me 80 Marks), where copying to tape was prohibitive, just to be repeated in the mid 2000s when DVDs where rolled out when CD writing became cheap and reliable.

The Long Read

To start with, CD production was, at that time mostly confined to 'real' CDs and in a factory setup, as writeables not only where prohibitively expensive, but also did not always produce a result readable on (cheap) CD-ROM drives. When looking at prices it may be helpful to see that CDs weren't a thing for computer users until 1991's Soundblaster Pro got sold with a special interface for the Mitsumi CD Drive (and often packaged with one). Keep in mind this is about games. Here only mass market counts, not some high power users like many of us may have been.

CD as a game medium only started after that. At this time their sheer size was the most relevant copy protection. Game companies where often accused of adding unnecessary content to explicitly bloat the size of data used - including lots of clips and cut scenes together with purposely non-compressed data, to make it hard to copy games onto disks. In fact, numerous game reviews did test games that where delivered as a 'basic version' on floppies as well as their 'enhanced' CD counterpart and found that the CD-version didn't add anything useful.

While the cost for a CD writer in the mid-90s dropped close to 1000 USD, that's still above the usual juvenile threshold. And writers still suffered from compatibility issues with regular (cheap) players. Even if daddy did invest in the son's future by buying a PC with a well-fitted SCSI based machine including a writer, media prices were comparably high. When bought as a 25 pack, a single writeable CD was close to 10 USD. Thus copying did still bear high cost.

The time argument doesn't matter so much on the hobbyist side, as waiting an hour for the CD to complete (*1) could be filled with whatever teenagers do anyway :))

It doesn't matter on a 'professional' scale as well. Just remember all the copying that was going on during early 80s with pirated video tapes. People had a dozen VCRs in their garage, hooked up to a 'Master' and copied in real time. More or less the same way with CDs in the mid to late 90s. Machines did run multiple drives at once, just this time the master was a hard disk. 8-12 drives per machine and 2-3 machines did make it a full time job. Heck, they even developed robotic handling (*2). Again, the media price was more of a limiting factor (and readability) than time.

At a 'professional' level the danger for game companies was rather on the side of real CD manufacturing, as a standard CD manufacturing machine could be bought for less than some high-end PCs. The only costly part was acquiring the glass master.

*1 - Whoever could at that time cash out for a writer, would always also buy a simple reader that goes with it, so transfer can be done in a single run.

*2 - A good friend of mine was into this. He did the garage business for video tapes in the early 80s, and after some ... err ... troubles, slipped again into it with CDs. He had an awesome setup with two small robot arms handling the CDs of two drives connected to a single machine. That way he could have it run 24/7. He said it was good business, but I still think if he had invested the time it took to develop the software and handling mechanics in a start-up for robotics, he'd be a wealthy man by now. I just wish I had secured that machinery for my collection.

It's probably not exact but Sony back in the day had a really cool way of Protection against pirates:

Simply said they changed the CD itself... and made it "Wobble" in a certain way in the beginning so the reader knew it's an OEM Disk.

In addition to Stephen Kitt's answer:

1. Copy protection existed long before CDs; most of these techniques could be applied to CD-ROMs too. Many games that were shipped on floppies had copy protection - sometimes a question in the beginning that asked you to look at the booklet it came with, Monkey Island had a disk with 2 parts that you needed to set according to instructions to get the right answer.


2. It was obviously much harder to distribute pirated copies then than it is now. The internet wasn't a thing so you were fairly limited in what you could acquire. Generally one of your friends had to actually buy the game. Sharing of games was fairly common, though.

A quick review of the games consoles suggests that the Saturn and PlayStation were the first to implement copy protection as a firmware-level feature; between the 3DO, Mega CD and PC Engine there are some measures to ensure games are from licensed developers but no built-in protection against copies. I was also unable to find any evidence of software for those platforms implementing its own protection schemes.

So the answer seems to be: during the first wave of dedicated games hardware, no substantial effort was put into copy protection; one can guess that it just wasn't considered to be likely to be feasible within the usual commercial lifetime of a console prior to about 1994.

Besides the measures against copying the CD-ROM there were other things.

Pretty popular were dongles: specific hardware devices put one the parallel port. The game (or other software) did not run without those dongles. The dongles could not be copied easily.

From what I remember - most successful was the Serial Number approach when every CD copy had a unique hash to verify the unit copy. Verification process would request a hash to validate the copy and flag it useable. Serial number was included as a sticker inside the CD package.