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iMac (Retina 4K, 21.5-inch, Late 2015) vs iMac (Retina 5K, 27-inch, Late 2015)

iMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2

Quick look

Quick look: iMac (Retina 4K, 21.5-inch, Late 2015) against iMac (Retina 5K, 27-inch, Late 2015)
FigureiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Price£1,1993launch price£1,4493launch price
ChipCore i53.1GHz quad-core IntelCore i53.2GHz quad-core Intel
CPU4-coreCPU4-coreCPU
Memory8GBmemory, base8GBmemory, base
Storage1TBstorage, base1TBstorage, base
Display21.5-inchdisplay27-inchdisplay
Released13 October 20153Released13 October 20153Released
Security updates16 September 20244Security updates ended16 September 20244Security updates ended
Price
The iMac (Retina 4K, 21.5-inch, Late 2015) is £1,199 at launch, per Apple Newsroom (UK); the iMac (Retina 5K, 27-inch, Late 2015) is £1,449 at launch, per Apple Newsroom (UK).

True to scale

iMac (Retina 4K, 21.5-inch, Late 2015) · 528 × 450 mm frontiMac (Retina 5K, 27-inch, Late 2015) · 650 × 516 mm front

Front faces, from Apple’s published dimensions, drawn to one scale and superposed. Corner rounding is our drawing convention, not a measurement.

Specifications

Each figure is from the source marked by its Mac’s name unless it carries its own small number, which links to where that figure was read.

Body

Body: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Dimensions450 x 528 x 175 mm516 x 650 x 203 mm
Weight5.68 kg9.54 kg
PortsTwo Thunderbolt 2 ports, four USB 3 ports, SDXC card slot, Gigabit Ethernet (RJ-45), 3.5 mm headphone jackTwo Thunderbolt 2 ports, four USB 3 ports, SDXC card slot, Gigabit Ethernet (RJ-45), 3.5 mm headphone jack
Thunderbolt ports22
Thunderbolt versionThunderbolt 2Thunderbolt 2
USB-A ports44
HDMINo HDMI port.5No HDMI port.6
SD card slotYesYes
Headphone jackYesYes
KeyboardMagic KeyboardMagic Keyboard
Touch IDNo Touch ID.5No Touch ID.6

Display

Display: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Display size21.5 in27 in
Resolution4096 x 23045120 x 2880
Display typeRetina 4K display with IPS technologyRetina 5K display with IPS technology
Wide colour (P3)Yes7Yes7

Chip and memory

Chip and memory: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Chip3.1GHz quad-core Intel Core i53.2GHz quad-core Intel Core i5
Apple siliconIntel processor, not Apple silicon.8Intel processor, not Apple silicon.9
CPU cores44
GraphicsIntel Iris Pro Graphics 6200AMD Radeon R9 M380 with 2GB of GDDR5 memory
Chip options3.1GHz quad-core Intel Core i5 or 3.3GHz quad-core Intel Core i73.2GHz quad-core Intel Core i5, 3.3GHz quad-core Intel Core i5, or 4.0GHz quad-core Intel Core i7
Memory (base)8GB8GB
Memory (maximum)16GB32GB
Memory options8GB or 16GB8GB, 16GB or 32GB
Memory upgradeable by userNo, as Apple documents10Yes, as Apple documents10
Storage (base)1TB1TB
Storage (maximum)2TB3TB
Storage options1TB hard drive, 1TB or 2TB Fusion Drive, or 256GB or 512GB flash storage (SSD)111TB hard drive, 1TB, 2TB or 3TB Fusion Drive, or 256GB, 512GB or 1TB flash storage (SSD)

Connectivity

Connectivity: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Wi-Fi802.11ac Wi-Fi802.11ac Wi-Fi
Bluetooth4.04.0
Ethernet10/100/1000BASE-T Gigabit Ethernet (RJ-45)10/100/1000BASE-T Gigabit Ethernet (RJ-45)
External displays (base)12

Camera and audio

Camera and audio: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
CameraFaceTime HD cameraFaceTime HD camera
SpeakersStereo speakersStereo speakers
MicrophonesDual microphonesDual microphones

Platform

Platform: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Shipped withOS X El Capitan12OS X El Capitan12
Newest macOSmacOS Monterey13macOS Monterey13
Model identifieriMac16,213iMac17,113
Model year20152015

Benchmarks

Benchmarks: Apple iMac (Retina 4K, 21.5-inch, Late 2015) against Apple iMac (Retina 5K, 27-inch, Late 2015)
SpecificationiMac (Retina 4K, 21.5-inch, Late 2015)1iMac (Retina 5K, 27-inch, Late 2015)2
Geekbench 7 (CPU, single-core)1,080141,08114
Geekbench 7 (CPU, multi-core)3,122142,90314

Sources

  1. Apple Support (UK) — iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification · Default for iMac (Retina 4K, 21.5-inch, Late 2015) · Apple’s figure · read 15 Sep 2026

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  2. Apple Support (UK) — iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications · Default for iMac (Retina 5K, 27-inch, Late 2015) · Apple’s figure · read 15 Sep 2026

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  3. Apple Newsroom (UK) — Apple Updates iMac Family with Stunning New Retina Displays · Apple’s figure · read 15 Sep 2026

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  4. endoflife.date — Apple macOS · third-party figure · read 2 Oct 2026

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  5. iMac (Retina 4K, 21.5-inch, Late 2015): No HDMI port. No Touch ID. Checked: Apple Support (UK) — iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification. Read 9 Oct 2026

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  6. iMac (Retina 5K, 27-inch, Late 2015): No HDMI port. No Touch ID. Checked: Apple Support (UK) — iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications. Read 9 Oct 2026

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  7. Apple Newsroom (UK) — Apple Updates iMac Family with Stunning New Retina Displays · Apple’s figure · read 3 Oct 2026

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  8. iMac (Retina 4K, 21.5-inch, Late 2015): Intel processor, not Apple silicon. Checked: Apple Support (UK) — iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification. Read 15 Sep 2026

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  9. iMac (Retina 5K, 27-inch, Late 2015): Intel processor, not Apple silicon. Checked: Apple Support (UK) — iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications. Read 15 Sep 2026

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  10. Apple Support (UK) — Install memory in an iMac · Apple’s figure · read 18 Oct 2026

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  11. Apple Support (UK) — iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification · Apple’s figure · read 11 Oct 2026

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  12. Apple Newsroom (UK) — Apple Updates iMac Family with Stunning New Retina Displays · Apple’s figure · read 9 Oct 2026

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  13. Apple Support (UK) — Identify your iMac model · Apple’s figure · read 15 Sep 2026

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  14. Geekbench Browser (Primate Labs) · third-party figure · read 11 Oct 2026

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Not published by Apple

iMac (Retina 4K, 21.5-inch, Late 2015). Apple doesn’t publish for this Mac: colours, pixel density, brightness, refresh rate, nano-texture option, GPU cores, storage upgradeable by user, maximum continuous power. Geekbench 7 Metal: the Mac chart has no Metal score for this Mac (chart read 10 Oct 2026). Pages checked: Apple Support (UK) — iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification; Apple Support (UK) — Identify your iMac model; Apple Newsroom (UK) — Apple Updates iMac Family with Stunning New Retina Displays, read 9 Oct 2026.

iMac (Retina 5K, 27-inch, Late 2015). Apple doesn’t publish for this Mac: colours, pixel density, brightness, refresh rate, nano-texture option, GPU cores, storage upgradeable by user, maximum continuous power. Geekbench 7 Metal: the Mac chart has no Metal score for this Mac (chart read 10 Oct 2026). Pages checked: Apple Support (UK) — iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications; Apple Support (UK) — Identify your iMac model; Apple Newsroom (UK) — Apple Updates iMac Family with Stunning New Retina Displays, read 9 Oct 2026.

If you own one of them

Whether to move is a different question from which is better. Each Mac has a page on it: what its successor changes (the newest Mac in its line where Apple sells one, otherwise the Mac this site treats as its replacement, which can be in another line), what it fetches and whether it still gets updates. Should I upgrade my iMac (Retina 4K, 21.5-inch, Late 2015)? · Should I upgrade my iMac (Retina 5K, 27-inch, Late 2015)?

The pairs a buyer of either Mac would also weigh. Any two Macs in the catalogue can be compared from the chooser.