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Apple launches new Retina 4K 21.5-inch iMac, all 27-inch iMacs now feature Retina 5K displays - 9to5Mac
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Amazon.com: Late-2015 Apple iMac 21.5 with 4K Retina Display/3.1GHz Intel Core i5-5675R Quad-Core (21.5-inch, 8GB RAM, 1TB) (Renewed) : Electronics
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Apple iMac with 4K Retina display (21.5-inch, 2015) review: Apple packs more pixels into its smallest iMac - CNET
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Review: Apple's 21.5" iMac with Retina 4K display gets solid 2017 architectural refresh | AppleInsider
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