Keeping the two OSes separated allows Apple to manage complexity in a way that Microsoft cannot when trying to merge three operating systems, for PCs, smartphones and the Xbox, into one core Windows 10 OS, Krewell said.
There are additional hardware challenges. Apple's devices with iOS run on homegrown ARM-based chips, and Macs run on Intel chips. To merge OSes, Apple may have to move its Mac OS over to ARM-based chips, which is no small task because the company is already pushing performance boundaries with its own chips.
"Apple had significant help from Intel in porting to the x86 architecture," McGregor said. "However, it is in Apple's interest to keep pursuing its own [chips] and to use them as widely as possible."
Apple will ultimately figure out where to draw the lines in the Mac-iPad divide. The market will tell the company how to position each product, McGregor said.
Apple's iPad shipments have been declining. The company shipped 16 million iPads in the first financial quarter of 2016, a decline from the 21.4 million units shipped in the same quarter a year earlier.
Tablet shipments totaled 206.8 million in 2015, declining by 10.1 percent from 2014, according to IDC. But shipments of hybrids like the Surface and iPad Pro are growing, IDC said.
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