Source: Apple.

Intel (INTC -0.80%) recently announced the highest-end members in its Broadwell family of processors aimed at high-performance laptops and potentially all-in-one PCs.

As I noted previously, Apple (AAPL -0.69%) skipped Broadwell for its 15-inch Retina MacBook Pro refresh and is likely holding off for Broadwell's successor, known as Skylake, to do a more substantial refresh of the device.

Apple didn't upgrade its iMac line of systems in its latest Mac refresh. It lowered the price on the top-end iMac with Retina 5K display from $2,499 to $2,299 and introduced a lower-end model at $1,999, but otherwise there were no changes to the lineup.

I suspect Apple will update its iMac products later this year. The question, then, is what processors will it use in the updated models?

The 27-inch upgrades should be all Skylake
The 27-inch iMacs generally use Intel's socketed Core i5/i7 processors. Since the rumors all point to an August launch of the comparable Skylake processors, I expect Apple to upgrade all 27-inch iMac models straight to Skylake.

The 21.5-inch situation gets a bit trickier
Although Skylake seems a "no-brainer" for the 27-inch iMac, the situation with the 21.5-inch models isn't as clear. Apple has two lines of 21.5-inch iMacs: standard and high end. The standard line uses a Core i5-4570R (per AnandTech), which is a quad-core part with Iris Pro graphics. This isn't a socketed (i.e., user-replaceable) part; it's soldered down on the motherboard.

However, AnandTech said the 21.5-inch high-end iMac comes with a Core i5-4570S. This part, unlike the 4570R, is a socketed part. It also doesn't feature the higher-end Iris Pro graphics, instead having standard Intel HD graphics. This is appropriate for the upgraded 21.5-inch iMac that uses a stand-alone graphics chip.

So why is this tricky to call? Well, because it's not clear if Intel will have a Skylake part suitable for the low-end 21.5-inch iMac around the same time that the other Skylake chips will be ready. The Skylake parts with the low-end GT2 graphics should be good to go around August or September, but will the parts with the higher-end GT4e graphics be ready?

If the answer is "yes," then I could see Apple doing an all-Skylake refresh of the iMacs in October. If the answer is "no," Apple might upgrade all of its iMacs to Skylake except the lowest-end 21.5-inch model. That system could either stay Haswell-based until the appropriate Skylake part is ready, or Apple could outfit it with a Broadwell part.

Will the GT4e part be ready in time for an October iMac refresh?  
This raises the question of whether the GT4e part will be available for an October iMac refresh. Looking at the Haswell launch schedule, Intel launched the socketed 2/4 core parts with GT2 graphics in June 2013 (at the very end of the second quarter). The 15-inch Retina MacBook Pro launched in October, but AnandTech tested production silicon of the four-core Haswell with GT3e graphics in June (suggesting the chip had qualified for production by then).

Indeed, a recent leak from BenchLife suggests Intel will launch the Core i7-6700HQ and Core i5-6300HQ chips in September 2015. In perusing Intel's processor database, I see that most of the chips with the "HQ" designation feature Iris Pro graphics (although there are some with standard Intel HD graphics).

This seems to indicate there's a decent chance Intel will have parts suitable for a low-end 21.5-inch iMac with fast on-die graphics by the time Apple is ready to refresh its iMac product lineup.