Hard Drive Relationships

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While working on my godson’s laptop, backing up his data (just in time, his hard drive clicked loudly a few times then died) I noticed that the cradles on my external hard drive dock are labeled “mother disc” and “son disc”.
Why not match the genders and label them “father disc” and “son disc” or “mother disc” and “daughter disc”? Or just “parent disc” and “child disc”?
Still, I guess it’s more PC than the hard drive terms I grew up with – “master” and “slave”.