Let's take a look at the hardware that allows 14.7 million pixels with a resolution of 5120 x 2880 on a 27-inch display:

Texas Instruments NH245 8-Bit Dual-Supply Bus Transceiver

Texas Instruments BUF16821 Programmable Gamma-Voltage Generator and Vcom Calibrator

Parade Technologies DP665 LCD Timing Controller

We assume this is an Apple modified version of the DP663 LCD Timing Controller

Texas Instruments TPS65270 Monolithic Dual Synchronous Buck Regulator

Texas Instruments TPS65168 High Resolution Fully Programmable LCD Bias IC for TV