iMac 27-in 5k

Processor
3.1 GHz

10th Generation Intel Core i5 6-core 3.1 GHz (Turbo Boost up to 4.5 GHz)

3.3 GHz

10th Generation Intel Core i5 6-core 3.3 GHz (Turbo Boost up to 4.8 GHz)

3.8 GHz

10th Gen 8-core Intel Core i7 3.8GHz (Turbo Boost up to 5.0GHz)

Memory
8GB (two 4GB) of 2666MHz DDR4 memory; four user accessible SO-DIMM slots
8GB (two 4GB) of 2666MHz DDR4 memory; four user accessible SO-DIMM slots
8GB (two 4GB) of 2666MHz DDR4 memory; four user accessible SO-DIMM slots
Storage
256GB SSD
512GB SSD
512GB SSD
Graphics
4GB
Radeon Pro 570X with 4GB GDDR5 memory
4GB
Radeon Pro 575X with 4GB GDDR5 memory
8 GB
Radeon Pro 580X with 8GB GDDR5 memory
Screen
Retina 5K display

27-inch (diagonal) Retina 5K display
5120 x 2880 resolution with support for 1 billion colors
500 nit brightness
Wide color gamut (P3)
True Tone Technology

Retina 5K display

27-inch (diagonal) Retina 5K display
5120 x 2880 resolution with support for 1 billion colors
500 nit brightness
Wide color gamut (P3)
True Tone Technology

Retina 5K display

27-inch (diagonal) Retina 5K display
5120 x 2880 resolution with support for 1 billion colors
500 nit brightness
Wide color gamut (P3)
True Tone Technology

Connectivity
3.5mm headphone jack
SDXC (UHS-II) card slot

Four USB-A ports

Two Thunderbolt 3 (USB-C) ports supporting:

DisplayPort
Thunderbolt (up to 40 Gb / s)
USB 3.1 Gen 2 (up to 10Gb / s)
Thunderbolt 2, HDMI, DVI and VGA compatible via adapters (sold separately)
Gigabit Ethernet 10/100 / 1000BASE-T (RJ-45 connector)

Kensington security cable slot

3.5mm headphone jack
SDXC (UHS-II) card slot

Four USB-A ports

Two Thunderbolt 3 (USB-C) ports supporting:

DisplayPort
Thunderbolt (up to 40 Gb / s)
USB 3.1 Gen 2 (up to 10Gb / s)
Thunderbolt 2, HDMI, DVI and VGA compatible via adapters (sold separately)
Gigabit Ethernet 10/100 / 1000BASE-T (RJ-45 connector)

Kensington security cable slot

3.5mm headphone jack
SDXC (UHS-II) card slot

Four USB-A ports

Two Thunderbolt 3 (USB-C) ports supporting:

DisplayPort
Thunderbolt (up to 40 Gb / s)
USB 3.1 Gen 2 (up to 10Gb / s)
Thunderbolt 2, HDMI, DVI and VGA compatible via adapters (sold separately)
Gigabit Ethernet 10/100 / 1000BASE-T (RJ-45 connector)

Kensington security cable slot