The Compact Disc may have been first prototyped in the 1970s, and the first CD-ROM drives available in the late 1980s, but it was the 1990s when CD-ROM games came to PCs. At first, however, they were little more than the same games on floppy disks with some kind of Redbook CD-Audio. Not long afterward, they were used to store digital audio in files and more detailed or higher resolution graphics and movies.
The first known CD-ROM game released for the IBM PC was The Manhole. This was a port of the floppy disk version of the B&W Macintosh original by Robyn and Rand Miller. The Millers would later go on to create Myst, but in the Manhole, you can see a definite beginning of the style of game for which they would become famous. The Manhole was released sometime around July, 1990. It supports VGA, MCGA, EGA and Tandy graphics. However, while the game uses VGA and MCGA graphics modes and supports a much wider variety of colors than the 16-color EGA and Tandy graphics modes, it displays no more than 16 colors on the screen at any one time. This was common back in 1989 when the floppy disk version was released, as using many more colors meant redrawing the graphics.
The CD format for The Manhole was a mixed-mode CD, consisting of one data track and one or more audio tracks. The CD standard can support a maximum of 99 tracks, and the Manhole uses 95 audio tracks (this does not count the data track) to store music, speech and sound effects. There is no need for a sound card to hear full audio with the CD version. Since there is no save feature, the game is run entirely off the CD-ROM. The floppy disk version supported Adlib, Roland MT-32 and Tandy 3-Voice music and Sound Blaster and Tandy DAC for speech. The audio is obviously much improved in quality and quantity over the floppy version. The graphics, however are exactly the same as the disk version. This version of The Manhole is very obscure today, and the game was re-released twice on CD-ROM format, once for DOS and Windows as The Manhole - New and Enhanced Edition (also on floppy) and once for Windows as The Manhole - CD-ROM Masterpiece Edition. These editions are much more common, much more impressive graphically, and use far fewer CD Audio tracks.
Just about one year later (1991), Sierra began to release its first CD-ROM conversions. While there probably were other games released beforehand, this was the first time a gaming company committed substantial resources and effort into promoting the new "multimedia" experience offered on disc. First came Mixed-Up Mother Goose, then Jones in the Fast Lane, followed by Stellar 7, King's Quest V and Space Quest IV. Like the Manhole, all had previously been released on floppies. They were also more expensive than the older floppy versions. Don't forget that a CD-ROM was a very expensive proposition in 1991, Sierra was charging $795.00 for a CD-ROM kit. At least the hardware, a SCSI CD-ROM and a Mediavision Pro Audio Spectrum (later 16), were high quality products.
Sierra's evolution of the CD-ROM format was simple. Jones in the Fast Lane included all its speech on one large audio track. The game would instruct the CD-ROM driver to play samples at specific times on the track. Music would require separate music hardware, as the only one CD-Audio track can play at a time.
Stellar 7 used its single CD-Audio track for speech during cutscenes for voice acting and the music. Sound effects were unchanged from the floppy version, relegating users to Adlib and MT-32 sound effects. One benefit to having all the music on one track was there would be less of a pause for the music to restart. However, preserving the timing of the track was especially critical, especially when making copies.
Mixed Up Mother Goose signalled a different approach. This time, the CD-ROM would be used strictly as a data CD, with the speech samples stored in one large audio file instead of on an audio track. A DAC like the Sound Blaster, Pro Audio Spectrum, Thunderboard, Tandy DAC or PS/1 Game/Audio Card would be required to hear the speech, which would be stored in an 8-bit sample format. Without this innovation, no more than 74 minutes of speech could be stored on a CD-ROM. Additionally, it was very annoying when the CD had to spin up to play a voice sample.
The most limiting aspect of the CD-ROM was the total inflexibility of pre-recorded audio. To adjust the parameters of a piece of music played on an MT-32, the programmer would only need to send a few kilobytes of data to the module. To adjust the music on a CD-ROM meant changing to another track. With 74 minutes maximum and 99 tracks, the musician could easily run out of space. LucasArts' games using the iMUSE dynamic sound system would always use the CD-ROM versions for voice acting.
Most CD-ROMs use the ISO-9660 format, which is standard for CD-ROMs and is widely used. Some of these early CD-ROMs, especially those from Sierra, use an earlier format called the High Sierra Format. MS-DOS's MSCDEX supports either format, but DOSBox has trouble with HSF. DOSBox will not IMGMOUNT a HSF image, but will MOUNT a drive using Daemon Tools and read the disc from that drive. Also, you can convert HSF images to ISO images using a program like Nero Burning ROM.
King's Quest V and Space Quest IV would continue the large audio file approach. A common approach to voices at this time was to use company members to voice various parts. Roberta Williams and other employees of Sierra, would lend their voices to many of these CD-ROM releases. Unfortunately, the resulting quality of the voice acting was somewhat lacking, since these individuals were not trained actors. Many other companies would follow Sierra's lead.
One company that never went the "Starring the programmers" route was LucasArts, which always sought professional voice talent for its CD-ROM conversions beginning with LOOM and Indiana Jones and The Fate of Atlantis. Professional voice actors had been relegated to roles voicing cartoon characters, announcers, bit parts and the like. Now there was a whole new avenue of employment for them for companies who cared enough about their expensive product to spring for decent voice acting. Eventually, "name" actors would be given roles.
Another type of CD-ROM release which began to appear in 1992 or so is the compilation release. On these CDs, there was nothing you could not have obtained on a disc, but the size of a CD allowed the inclusion of several (older) games (Interplay 10th Anniversary) or a game and all its expansion packs (Wing Commander Deluxe).
Data compression and relatively low bitrate techniques helped keep the size of speech files in check, and companies began to put full motion video on their discs. Interplay would re-release its Lord of the Rings : Fellowship of the Rings with animated scenes taken from the Ralph Bakshi movie of the 1970s. Sierra King's Quest VI CD-ROM would include a longer, better animated version of the introduction contained in the previously released floppy version.
One final issue with CD-ROMs games of the time is that these versions always seemed just to have something goat-glanded onto the floppy version. When the 7th Guest turned out to be a huge hit in 1993, all of a sudden the market for CD-ROM only games became attractive to developers. The 7th Guest used high resolution graphics throughout, digitized video around every corner and plenty of voice acting. It also came on two CD-ROMs. Far too much would have had to be cut to put the game on floppies, so Trilobyte took a gamble and did not bother to release a floppy version.
Just after The Seventh Guest, LucasArts released Day of the Tentacle simultaneously on floppy and CD. Up to this point in time, CD releases would lag several months behind floppy disk releases. Additionally, by the time the CD was released, there would be interface changes and the like. For DOTT, the game was more or less identical except that the CD version had a very large audio file. Floppy users still had the benefit of speech during the opening scenes. By the end of 1993, many, many games were being designed with CD-ROM first and then a cutdown floppy version would follow, usually compressed onto many disks.