I found this graph, and the percentage appears to be lower then 10%Macs account for less than 10% of Apple's revenue - and that's including all Macs, i.e. MacBooks, iMacs, Mac minis etc.
You raise a good point regarding where the Mac sits within Apple's revenue
Macs account for such a small percentage of revenue, one could make the argument that it may not mke financial sense to invest in 10s or 100s of millions on a chip design dedicated to the Mac Pro (or a dedicated desktop chip). What is sad, and disconcerting is that wearables have surpassed the Mac and the iPad is nipping at its heels.
I'm not sure if anyone remembers but there was supposed to be an Extreme version of the M series chip that was supposed to go into the Mac Pro (rumored to be two Ultra chips lashed together) but apple scrapped that, as there were technical challenges they could not over come.
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