How does the algorithm that controls the computer's LED signaling the process of accessing the hard disk work?

Question

Hard disks

I am developing a device that works with memory and I would like to inform the user about this procedure in the same way as a computer LED informs about communicating with a hard drive. But by what algorithm does this LED blink?
Depending on the fullness of some (rx / tx) buffer, does the LED PWM with a certain filling? Or does it just glow for a certain time (for example, 1 ms) for each byte passed through the interface?
Google didn't come up with clear results.

Answer 1

On old (very old) drives, the diode was an important indicator that the system was busy and working with the drive - then the drives were quite leisurely. On more modern drives, which are also old, but already exist, for example, in our collection, there were pins to which a diode could be connected directly.

Depending on the fullness of some (rx / tx) buffer

Now, I believe, the diode also lights up when the state of the disk changes to "busy". This is confirmed, at least, by dead hard drives - if the disk is dead and hangs in a busy state, then the indicator lights up continuously.

Google didn't come up with clear results.

If there is no information about drives on google, it might be worth looking for the same, for example, about network cards (and related equipment)? They have a similar diode that blinks when data is transmitted.
By the way, I soldered in parallel to the LED of the network card in the best years, when there were still "Sleep LED" on the cases - both indicators blinked, although the brightness decreased slightly.

Answer 2

https://habr.com/ru/post/29194/

An interesting idea is circulating on the Internet: to install a sound system, a small speaker and a small program on each data center server that utters a random curse when each gigabyte passes through the network card.
Imagine - a data center, darkness, and only the servers in the racks are swearing quietly.