When you hook one of LG’s 5K monitors to one of the new MacBook
Pros, what you’re actually seeing on the screen is two pictures
stitched together to make a single seamless image. This is because
the version of the DisplayPort spec supported by Intel’s GPUs and
almost all monitors these days — version 1.2 — doesn’t have
enough bandwidth to drive a 5K display at 60Hz all by itself. This
will change with DisplayPort 1.3, which is right on the cusp of
going mainstream, but it’s not here yet. Apple is actually pushing
two DisplayPort 1.2 streams to the monitor over the single
Thunderbolt 3 cable.
These kinds of workarounds were common in the early days of 4K
displays before the DisplayPort 1.2 spec went mainstream, although
you’d typically actually need two physical DisplayPort cables to
make it happen. Apple actually uses a variation of the same idea
for the 5K iMac’s internal display.
There’s nothing wrong with this method, except that it cuts down
on the number of external displays your computer can support.
Intel’s integrated GPUs can drive a total of three displays, but
you use up two of those three streams to drive one 5K monitor and
one of them to drive the laptop’s internal display. AMD’s GPUs
support up to six displays, so you can use two of those
connections for one 5K monitor, two of them for the other 5K
monitor, one for the laptop’s internal display, and still have one
left over for yet another monitor if you really wanted to use one.
This is why the 13-inch Pros can only use one 5K Thunderbolt
display and the 15-inch Pros can use two of them, and it explains
why Apple chose to go with AMD’s GPUs across the entire 15-inch
lineup. It’s difficult enough to explain the differences between
the $1,499 “MacBook Escape” and the model with the Touch Bar;
imagine how much more complicated that becomes if you’re selling
some 15-inch models that can drive two 5K monitors and some that
can only drive one.
If you’re looking for a review with a thorough set of benchmarks — CPU, GPU, SSD, and more — this one is it. There’s quite a bit about the new MacBook Pro with function keys that’s different from its Touch Bar equipped siblings — the “MacBook Escape” feels apt.