CD tech specs
The Compact Disc, or CD for short, was the first popular digital audio format. It built upon two existing technologies from two different companies.
Philips had enjoyed modest success with their 12" LaserDiscs, which were read with a laser and stored a read-only analogue video, such as part of a film (which spanned both sides of multiple discs, due to the format's low capacity). They shrank them down to 12 cm to make the physical aspect of CDs.
Meanwhile, Sony had also enjoyed modest success with storing digital PCM audio waveforms on analogue videotapes, first in music studios using big U-Matic tapes with the PCM-1600, and then in consumers' homes using smaller Betamax tapes with the PCM-F1. The waveforms were stored as black and white pixels on the videotape, and the 16-bit 44.1 kHz quality was straightforward enough to store on both PAL and monochrome NTSC tapes.
Working together, Philips and Sony combined their knowledge to store the digitised waveforms more directly onto the small optical discs, bypassing much of the intermediate layer of analogue video compatability. This was a format intended specifically for digital audio. It became the "Red Book" standard, the original Compact Disc.
As CDs could store over half a gigabyte of data, it made sense to use them to store any arbitrary data, not just audio. As CDs could originally only be made at pressing plants, pre-recorded and non-editable, data CDs were known as Compact Disc Read Only Memory, or CD-ROM for short, much like the ROM chips of home computers. The CD-ROM spec was finalised in 1983, and published in 1988, as the "Yellow Book" standard.
This standard didn't specify a filesystem. For a few years, any given CD-ROM could contain just about any format of data. For example, in the 1990s there was a niche industry of sample CDs, using the native filesystems of various samplers, such as the Akai S1000. Via a SCSI CD-ROM drive, a sampler could read a CD-ROM the same way it could read and write to a SCSI hard drive.
To this day, if you really want to, you can still write any filesystem, or even a single file, directly to a CD-R. (Unix-based systems tend to be good at this, generally having a modular and low-level approach to tasks. For example, you can simply use
dd to copy a CD-ROM to a single binary file, whatever its filesystem.)
People soon realised it would be a good idea to have a single standard filesystem for CD-ROMs. They chose the lowest common denominator between each computer's own native format, so everyone could read these shiny new discs. The result was ISO 9660, also published in 1988, which imposed DOS-style limits of up to 8 uppercase letters, numbers and underscores for directory names and filenames, and 3 for filename extensions.