The 2011 27” iMac is a great machine because of its lovely monitor, a range of connectivity options, all in one form factor, and, compared to other models with the glued-shut assembly, relative ease to open up and do maintenance and mods.
The GPU is the troubled piece in the 2009-2011 models and that is a shame because plenty of graphics cards failed and caused users to dump machines. Fortunately, they can be had for $100 or less in this state or maybe turn up in eWaste bins, and for a DIY person with a few bucks to sling around, it can be a great project that will bring a fine machine back to workable life. Other mods and updates are helpful.
Originally the iMac had 2.7 and 3.1ghz CPUs and the i7 3.4 Quad was a configure-to-order item. They are cheap and a great upgrade if you have one of the others.
There is a “K” model that is not the right one. No K, OK?
2nd Gen Intel Core i7-2600 CPU 3.40GHz (Turbo 3.80GHz) 4-Core 8MB LGA-1155 SR00B
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https://www.intel.com/content/www/us/en/products/sku/52213/intel-core-i72600-processor-8m-cache-up-to-3-80-ghz/specifications.html
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GPU mod overall concept and steps. This Macrumors forum post is the bible for this mod. It’s been around since 2013 and the first post is now a detailed Wiki to expedite making sense of years of experiments.
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https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/page-596?post=29967927#post-29967927
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There are NVIDIA fans and AMD fans. I can’t comment on the AMD cards but I’ve done three mods on different iMacs using NVIDIA K2100m and K4100m cards. I’ll vouch for each of these being reliable since my first (K2100m) was in late 2020, second (flashed K4100M) in summer 2022, and another K4100M I decided to flash myself on a third upgrade in early 2025.
Flashing is not hard but it is one of those intimidating steps that may not be for everyone. It requires a second Mac and some rudimentary Linux use. For some money it may be worth just finding a flashed card. I will praise Newell Technology for being a vendor who flashes for the very purpose we’re doing this: to retrofit an old iMac. Newell knows his stuff, expects people like us with our questions, is responsive, and while more expensive for providing the flashed cards, is a get-the-job-done-right-the-first-time option.
Basic page for the 4100.
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https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/page-319?post=28692959#post-28692959
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K4100m used in September 2022 mod. Same vendor has other powerful cards for iMac modders like us, including the 880.
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https://newelltech.tech/shop/ols/products/xn-231277128-apple-imac-27-a1312-nvidia-quadro-k4100m-4gb-mxm-video-card-gpu-replace-6970m-1n59c
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2011 iMacs can have up to three internal drives. If you want to go all-SSD it just requires a few pieces of hardware.
OWC Data Doubler to replace optical drive with a second SSD.
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https://eshop.macsales.com/item/OWC/DIDIMCL0GB/
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There’s a secret SATA port where you can add another (third) SSD sandwiched behind the optical drive. Requires extensive logic board preparation to pivot back, or total removal.
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https://eshop.macsales.com/item/OWC/DIDIM27SSD11/
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