Technically a "configure-to-order" version of the iMac "Core i5" 3.1 21.5-Inch Aluminum (Retina 4K, Late 2015/Broadwell), the iMac "Core i7" 3.3 21.5-Inch is also listed as a separate model for clarity. Except for the processor and its corresponding L3 cache, the two models are identical.
This iMac features a 14-nm "Broadwell" Quad Core 3.3 GHz Intel "Core i7" processor (5775R) with four independent cores on one chip and a 6 MB shared L3 cache. It includes 8 GB of onboard 1867 MHz LPDDR3 SDRAM (upgradable to 16 GB only at the time of purchase), a 1 TB (5400 RPM) hard drive, and an integrated Intel Iris Pro 6200 graphics processor that shares system memory. It also has a built-in "FaceTime HD" webcam and stereo speakers.
It sports a 21.5" 4096x2304 LED-backlit 16:9 widescreen IPS "Retina 4K" display, which runs "pixel doubled" to appear as 2048x1152. The rear aluminum case is thicker at its center and tapers to a slim 5 mm at the edges. Connectivity options include four USB 3.0 ports, dual Thunderbolt 2 ports, Gigabit Ethernet, 802.11ac Wi-Fi (compatible with 802.11a/b/g/n), and Bluetooth 4.0.
Compared to its predecessor, this model shares a nearly identical external design but offers a significantly higher quality and resolution "Retina" display, along with a more advanced architecture and graphics. The "Late 2015" iMacs were shipped with a compact aluminum Apple Magic Keyboard and a choice of a multi-touch "Magic Mouse 2" or a conventional wired Apple mouse. An optional US$50 upgrade to the "Magic Trackpad 2" provided multi-touch and pressure-sensitive "Force Touch" capabilities.