I dont think it changes rotational speed…
There’s another thread on this forum that talks extensively to your question…
Also, FWIW, There are 3 flavors of Western Digital drives. Black, Blue and Green. Black is considered the “industrial strength” version. Intended for things like servers etc… It’s a solid drive but uses a constant speed seek method (the read write heads always move at max speed) that can make it rather noisy…lot’s of clicking, and tends to run a little warmer.
The blue drives are what I use. Lower cost and they use a read/write head seek algorythim that calculates how long it’s going to take for a particular sector of the disk to come around to the heads and moves the heads just quick enough to get there in time. Reduces noise, lower power req’s and lower heat. Possible longer life span due to less wear/tear on the heads.
Green are the eco- version drives. Good for large capacity back ups but not ideal for DAW use. Slow data xfer rates.
There’s a free bit of software you can download from the web called HDTune. Nice package that will run diag’s to your hard drive system and show you dtat xfer rates etc… Handy for checking your hard disk performance.
All the best,
Karl