As best as I understand it, we can start with thinking about it in terms of a music vinyl disc. For the sake of ease, let’s say that a vinyl is 60 rpm, or one r

As best as I understand it, we can start with thinking about it in terms of a music vinyl disc. For the sake of ease, let’s say that a vinyl is 60 rpm, or one revolution every second to “read” the song. (It’s actually about half that.) This is somewhat similar to how a “music cd” works and is why you can only get around 70-80 minutes of music on a CD that can hold hours of that same music in a compressed data format. The audio is uncompressed, therefore much like a vinyl. This establishes our 1x speed, in this case using one revolution per second. Now to the speed differences. To read, the laser needs only to see a reflection (or not) at a specific point, while to write, the laser needs time to heat up that same point. It’s like the difference between seeing a laser reflect off a balloon, versus the time required for that same laser to pop it. This heating is how CDs are written, quite literally by heating up points on the disc until they are no longer reflective. That’s why it is called “burning”. While more power might speed up the process, there is still time required. Meanwhile, all that is needed to read faster is an increase in the speed to observe, or the frequency to “read”, the light reflection. With more powerful lasers operating at a faster frequency and with more precision, we can have a laser “see” these differences at 48 times the normal speed, but can only burn at 8 times the normal speed before the reliability of the process suffers. Bonus: for a rewritable disc, it works slightly different. Instead of destructively burning the CD, you can think of it as being a material that becomes non-reflective at one temperature, and reflective again at another. This allows data to be “erased”. Also, when you “close” a disc to prevent rewriting, you aren’t actually preventing it from being rewritten. It is more like using a sharpie to put a name on the disc, with the words “do not overwrite” that all drive software/firmware respects.