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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?

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    Don't forget the increase in speed of the receiving end. A late 1980s computer would probably have trouble to do anything useful of 6 MBytes/sec.
    – UncleBod
    Oct 4, 2022 at 14:52
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    @UncleBod Fast SCSI-2 was around by then. Though true that was for high-end computers, not "budget" PC's.
    – Brian H
    Oct 4, 2022 at 15:06
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    I suspect the apparent exponential rise is a red herring, and there were actually a series of step changes, as different problems were overcome. Going from "as fast as necessary for audio" to 2x or 4x may have been trivial; then different approaches to precision and balance were needed. There were many rumours of 12x being the limit above which damaged disks would explode under vibration.
    – IMSoP
    Oct 4, 2022 at 16:08
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    Same reason why cd drives never really went above ~48x or so. Too much of a chance of the disk exploding...
    – TLW
    Oct 4, 2022 at 23:43
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    It's kind of strange that we allowed 5.25 plastic discs to go beyond 10000rpm while 3.5 hard drives never exceed 7200rpm. Oct 6, 2022 at 4:12

1 Answer 1

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While reading a CD, the main head assembly will simply move slowly from the inside of the disk outward, but unless the disk is absolutely perfectly centered--something that usually doesn't happen--the laser head itself will need to move in and out with each rotation in order to follow the track. Early CD mechanisms were designed to accommodate about five in/out wobbles per second, but spinning the disk faster will make it necessary for the head to move faster while following the tracks. Beyond the higher mechanical requirements, this poses another problem: at slower speeds, the head could move in response to indications that the beam was on one side or the other from where it "should" be, but as speeds increased it became necessary for the head positioning electronics to "predict" how the track would move, so as to need only small adjustments beyond that.

Another factor is that I don't think drive manufacturers really knew how fast drives could go without creating a risk that poorly manufactured CDs might explode catastrophically in such a manner as to destroy not just the disk, but also the drive as well. In many cases drives from more established brands wouldn't achieve speeds quite as high as those from lesser-known brands, which would compete on the basis of their higher speeds. If a lesser-known brand whose top spin rate was e.g. 4000RPM (compared with a normal "1x" top speed of about 500RPM) was on the market for a few months, and there were no apparent complaints despite the fact that consumers of budget drives might be more likely to use lower-quality media, then name brands could figure they could safely use comparable speeds.

From a practical standpoint, most drives ended up being limited to about 8000 RPM, which is 16 times the speed of a 1x drive when reading data near the center of a disk. Because one rotation's worth of the spiral track near the edge of the disk could hold about 2.5x as much data as one rotation near the center, and drives could maintain the 8000RPM speed even when reading data that was further out, such drives could read data near the edge of the disk 40 times as fast as a single-speed drive could, and were thus marketed as "40x drives".

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    I think the general story here is probably about right, but the "watch and see if people complain" methodology seems slightly implausible. More likely, it was a case of "stress test and release to market with a known safety tolerance". Cheaper brands might be more likely to cut corners on that testing and push the boundaries for a quick buck, but ultimately the mechanical problems of balance and precision were what needed to be innovated.
    – IMSoP
    Oct 4, 2022 at 15:52
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    Wouldn't spinning the disk faster tend to reduce the amount of "wobble" because inertia?
    – Brian H
    Oct 4, 2022 at 16:05
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    @BrianH: If the center of the spiral coincided with the center of mass of the disk, the spinning mechanism was on a lightweight free-floating suspension, and there were no issues with resonance, then spinning the disk faster could reduce the distance the head would have to move to follow the track of an off-center disk. That's a lot of "ifs", however. Increasing rotational speed will increase centripetal acceleration and make it harder for bearings to accommodate it smoothly. Worse, any imbalance will like cause the axis of rotation to tilt slightly, setting up nasty resonance effects.
    – supercat
    Oct 4, 2022 at 18:02
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    @davidbak: Writing a disk at 8x speed requires a more powerful laser than writing at 4x speed, but not exactly twice as powerful. Using too much laser power will create spots that are too big to be read reliably, while using too little will produce spots with insufficient contrast. From what I understand, drives that could write media with just the right characteristics at 16x speed, and media that could be written at 16x speed by drives with just the right characteristics, were created before there was any standardized way of characterizing drives and media to ensure compatibility.
    – supercat
    Oct 4, 2022 at 20:01
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    At least the bigger brands didn't market their drives as "40x", but marked it " 40x max" instead because it's just the maximal rate the drive can achieve, not the rate it will get everywhere (as it was on CLV drives like 4x drives). Customers didn't notice the distinction between 6x (CLV) and 16x max (CAV), though, so the 16x drive sounded nearly thrice as fast. Oct 4, 2022 at 20:26

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