Early CD-ROM drives were considered both expensive and slow (in comparison to HDDs). This limited their adoption until around 1992, when both the prices fell and the speeds increased dramatically.
In the mid 90s (roughly 1993–1997), I recall CD-ROM speeds increasing very rapidly; probably doubling in speed every 6–12 months. I got my first PC, which included a 2x CD-ROM drive, in 1993. And it seems that 32x drives were the normal option by 1997–98, even for "budget" PC's.
For perspective, the original 1x CD-ROM's of the late 80s transferred data at 150 KiB/s, while a 40x drive from the late 90s would do 6000 KiB/s.
I know that, fundamentally, the speed up is down to higher rotational speeds. However, the pattern of doubling of performance, and at a high rate, suggests the innovation was probably in the digital circuity. Like better error correction or better peripheral interfaces to the CPU. Though, maybe it was just about tweaking the analog aspects (motors, optics) instead? It seems weird to me that small spinning motors would be an innovation area in the 1990s, especially after so much of that had already been perfected for hard drives; additionally, the apparent exponential rise in the speeds.
So where were the innovations happening during this interesting period: motors, laser/optics, digital circuitry? How is this rapid speed increase best understood?