Why do my 2 laptops have 2 hard drives c and d?

I have a very new mini laptop with solid state hard drives,, but the drive c was almost full, and I had to free up a bit of space to avoid getting warning notices, but drive D is almost empty! What is the purpose of 2 drives as we have a 3 year old laptop with only 1 drive, also can programs be installed,moved or... show more I have a very new mini laptop with solid state hard drives,, but the drive c was almost full, and I had to free up a bit of space to avoid getting warning notices, but drive D is almost empty! What is the purpose of 2 drives as we have a 3 year old laptop with only 1 drive, also can programs be installed,moved or down loaded on to drive d ? Many Thanks...
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