Clearly that will depend on their launch date and the hardware that's available at the time. After Skylake, the next round of Intel processors, going into mass production in late 2016, will be Kaby Lake, followed in turn by Cannonlake (Cannonlake was due to be next, but it's been delayed until the second half of 2017). Then Ice Lake in 2018 and Tiger Lake in 2019, for those who enjoy this sort of thing.
Kaby Lake uses a 14nm process, same as Broadwell and Skylake, but Cannonlake switches over to a more accurate 10nm process.
If Apple does manage an iMac update before the end of 2016 the machines could feature Kaby Lake processors, but remember that Apple skipped Broadwelland delays are common the chip sector - so we're not banking on anything.
It's believed that Apple's next generation of iMacs (or the higher-specced models, at least) will feature graphics chips from AMD's Polaris set, which were announced at the start of 2016.
WCCF Tech reports that AMD won the contract last October but was only able to get confirmation from additional sources in April 2016.
The contract is for two chipsets: Polaris 10 (previously known as Ellesmere) and Polaris 11 (previously known as Baffin), and WCCF Tech says these processors will appear in "new desktops and notebooks from Apple, which the company plans to bring to market later this year".
With the MacBook and MacBook Air having recently seen updates, and the Mac mini highly unlikely to incorporate a discrete graphics unit, the remaining candidates are the MacBook Pro, iMac and Mac Pro. MacRumors reasons that the power range of these chips makes Polaris 11 a strong fit for the MacBook Pro, while Polaris 10 suits the iMac.
The Polaris chips offer a ramp-up in graphics performance over previous generations (as much as twice the speed per watt) and potential reductions in both power consumption and waste heat. They are built using a 16nm or 14nm FinFETproduction process, compared to 28nm on AMD's earlier chips, which means that the chip maker can fit more transistors in a given space (which makes the chips ideal for ultraportable laptops and ultraslim desktops - the latter fittting recent iMac designs) and, because the transistors are closer together, less power is needed to move a signal across them.
Apple's current iMac line-up features AMD Radeon graphics chipsets as standard in the 27-inch models. The 21-inch models come with integrated Intel Iris Pro 6200 graphics.
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