My D: drive downloads things way slower and clunkier than my C: drive

I'm not really that knowledgeable about tech stuff, so I am unsure if this is normal,

but while downloading videos, games or any kind of files onto my C: drive, it's easily capable of reaching the maximum download speed that my internet speed allows (600 mbps), with rarely any significant drops.

However whenever I try to download things onto my D: drive, it's barely able to get to the speed of my other drive, getting around 70 mbps with constant drops to 0 (especially on platforms like Steam)

My C: drive is an SSD while D: drive is HDD, which I assume is the main reason for their different download speeds, however I don't know if there is a way to boost the performance of my D: drive.

Tried looking this up on the internet, but none of the forum posts I saw seem to be coherent with each other and they all give a completely different answer.

Is this normal? And if so, is there any way to boost the performance of the D: drive?