Mac prompted Rufus to produce a Mac clone. Rufus had shown he had the skills when he'd updated and miniaturised Mac from Marcus's original unportable prototype.
Using the university's facilities, Rufus cloned Mac. But it was more than a clone as it used even faster processing and twice the memory. It wasn't just another Mac in a different skin. It was an upgrade.
Naturally, Rufus decided to use the new improved version, but felt, prompted by Mac, he needed to store old Mac somewhere safe.
Mailing it to himself at his mother's house, he told her to keep it safe.