Parts for Apple Retina 4K (4096 x 2304) Retina 4K (4096 x 2304)

This model has a 21.5" 4096x2304 LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 4K" display (that runs "pixel doubled" to look like 2048x1152). The rear of the case is aluminum and is thicker in the middle and tapers to a razor thin 5 mm at the edges.
Connectivity includes four USB 3.0 ports, dual Thunderbolt 2 ports, Gigabit Ethernet, 802.11ac Wi-Fi (802.11a/b/g/n compatible), and Bluetooth 4.0.
Compared to its predecessor, this model essentially has the same external enclosure, but it has a vastly higher quality and higher resolution "Retina" display as well as a more advanced architecture and graphics architecture.
The "Late 2015" iMac models ship with a compact aluminum Apple Magic Keyboard and the choice of either a multi-touch "Magic Mouse 2" or a traditional wired Apple mouse. For an additional US$50, one also can upgrade from the Magic Mouse 2 to the "Magic Trackpad 2," which provides multi-touch and pressure-sensitive "Force Touch" capabilities.