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The Reason Apple dropped iMac14,2 from Big Sur Supported Macs

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trs96

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When Apple announced which Macs would still be supported by macOS 11, I found it hard to believe they dropped support for 2013 iMacs and kept support for the 2013 MBP and 2013 Mac Pro. There seemed to be no good reason to drop the Late 2013 iMac from their list of supported Macs. It's more than capable of running Big Sur, especially if a 2014 Mac mini is able to. It looks as if they use other criteria to determine which Macs can install and run the latest macOS.

After a good amount of research, it's clear to me now that Apple drew the line for Big Sur support at Desktop Macs and Macbook Pros that have Thunderbolt 2 controllers. The Mid 2014 15,1 iMac has TH2 ports, the 14,2 iMac doesn't. The Late 2013 iMac was announced, 9/24/13, just before TH2 was ready to be included in a Mac. The late 2013 MBP was released in the latter part of October that Fall and had TH2 ports. The first Mac to ever have them. That's why the Late 2013 MBPs get Big Sur support. The Mac Pro 6,1 of course, didn't ship until late December of 2013.

The Late 2013 27" iMacs have more than adequate GPU and CPU performance to run Big Sur, it's just that they were stuck with the older TH1 1st gen ports. The 2013 Mac Pro 6,1 has 6 TH2 ports so it made the cut for Big Sur.

Screen Shot 26.jpg

The 2014 Mac mini has TH2 ports onboard and a low power dual core laptop CPU. It has a 5400 RPM HDD. Those are considered Big Sur capable. Can't imagine how painfully slow one would be with Big Sur installed. Would certainly require an SSD upgrade to be usable.

The following models are Thunderbolt 2 capable:
  • MacBook (2015+)
  • MacBook Pro (Late 2013+)
  • Mac mini (2014+)
  • iMac (2014+)
  • iMac Pro (2017+)
  • Mac Pro (2013+)
The iMac 21.5" from mid-2014 makes the cut even though it's got a dual core laptop CPU with HD5000 graphics. Not nearly as capable as a 27" Late 2013 iMac with dedicated graphics (Nvidia GT 755M) and a quad core i5-4570 or 4670. Try comparing GeekBench scores between the two CPUs and you'll see that the quad core i5 is significantly ahead.

Screen Shot 28.jpg



The main difference between Thunderbolt 1 and 2 is that version 2 has channel bonding and DisplayPort 1.2, for full 4K video support. Whereas Thunderbolt 1 has two independent 10 Gb/s channels, Thunderbolt 2 combines these to give one 20 Gb/s bidirectional channel. This leads to more efficient transfers, with less overhead, but the total bandwidth is unchanged. Apple seems to think that these differences are important enough to drop the TH1 based 2013 iMacs.
 
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trs96

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The one Mac that Apple did give a Big Sur pass, the Macbook Air, mid 2013, only has a single TH1 and not a TH2 port. Intel only announced TH2 in June of 2013 so there's no way they could have included it in the MBA Mid 2013 edition.

These are primarily media consumption, internet surfing, ultra thin laptops. As 9to5 Mac said in their review: "The Air is meant to be a portable machine, not something you hook up to all your peripherals and monitors." They do have Intel HD5000 graphics which were the cutoff point for igfx that work with Big Sur. Every Mac with Intel HD4000 igfx and older didn't get support in Big Sur. If your CPU does have HD4000 you may still be able to get it to work by switching to Mac Pro 6,1 SMBIOS. Many have done this with success with the Big Sur Public betas.

The other good news is that those with Haswell based hackintoshes that rely on HD4600 graphics can still install and use Big Sur by changing their SMBIOS to iMac 15,1 if they haven't already. When you use the ig-platform-id 0300220D macOS Big Sur sees your graphics as Intel Iris Pro 5200 which are still fully supported. Then you can power a display via your onboard DP or HDMI output. You can even run a 4K display from an onboard DP 1.2 output.

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CaseySJ

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This makes sense and is consistent with previous end-of-support decisions. For example, Yosemite dropped support for Intel processors without a particular AVX instruction set (if I recall correctly) such as my 2008 Mac Pro. That, ironically, was the spark that led me to Hackintosh because in late 2018 there were no Apple products comparable to the retired Mac Pro.

I’ve also noticed that Big Sur no longer contains the drivers for Apple’s own Thunderbolt Gigabit Ethernet adapter (based on older Broadcom chipset). Apple also uses Broadcom chipsets in the formula for determining what to obsolete. Mac models with certain older WiFi/BT chipsets are also added to the chopping block.
 
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If one were to upgrade to Big Sur by changing the smbios with a system with thunderbolt 1, would thunderbolt 1 still be operational or would it not even be recognized altogether?
 
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