Investigation: Why is Bootcamp so much worse on the 2020 Air?

I've owned a 2020 i5 MBA and currently own a 2020 i3, and Bootcamp has been a nightmare on both compared to the 2019. Mostly in terms of battery life - you can watch it tick down before your eyes. But there are also issues in regards to realising the Ice Lake/Iris Plus performance boosts, making the Windows experience functionally the same as on the less powerful 2019.

So, the easy answer to 'why is Bootcamp not very good' in any discussion is 'because Apple doesn't bother optimising drivers', and whilst that's true it's not exactly helpful to people who require Bootcamp and Windows 10 for whatever reason.

I've been doing a fair bit of work this weekend and I've identified some issues, if not fixes just yet.

Partially Solving Apple's Driver Issue

First and foremost, I'm not aware of any OEM who does an excellent job with out of the box drivers, but Apple really takes the cake. The Windows Support Software package that is installed after a Bootcamp partition is made contains some drivers from 2006, out of date drivers for the Iris Plus GPU, and no software to run for updates and install them.

So I did, manually, and (especially with updated Intel drivers) noticed increased performance in graphics, from colour reproduction to hardware-assisted rendering of web pages. It's not a silver bullet, but it does offer noticeable improvement - it's just a shame Apple makes this so hard to do.

I normally avoid non-OEM driver updaters like the plague, but given Apple doesn't provide a solution, Driver Booster is the best option. It doesn't install a bunch of third party crap and even though it bugs you to get the paid version, you're able to accomplish a lot with the freeware trial.

The big problem - processor C-states and battery life

The 2019 Macbook Air on Windows 10 is able to comfortably get 9 hours battery life doing simple tasks. The 2020 (i5 and i3, as I've tested them) is barely able to hit 6.

After a lot of messing around and using Throttlestop (not recommended unless you have experience undervolting Intel CPUs/Windows 10 tweaking in general), I think I've been able to identify the big issue with the help of some very smart people over at Notebookreview.

Probably the easiest way to think of C-states is like gears in a manual car. The lower the gear (C-state), the more direct power you're able to give a particular task, but also the less efficient your fuel consumption (battery) is.

Intel's datasheet for Ice Lake chips (published April 2020) states that the 10th gen chips should all have a full gearbox - in this case, access to C0 (launching), C2 (hard work), C3 (light work), C6 (cruising on the highway) and C7 through to 10 (your engine is now so efficient you're barely using fuel).

Unfortunately, the 2020 MBA running Windows 10 can only access C2 and C3, meaning the processor is drawing much more power than it should and is being prevented from entering deeper sleep states. For comparison, the lowest C-state the Y-series 8th gen chip in the 2019 MBA can enter is C6, but it parks about 90% of its load there, making for very efficient running.

Without access to C6, the 2020 MBA running Windows is like constantly driving in second and third gear - sure, it's powerful and responsive, but it's incredibly energy inefficient.

I'm doing some work to attempt to identify a) if this problem can be solved and b) if so, what's the best method. On paper, the 2020 i3 should easily be able to match or come close to the 2019 i5's battery performance and longevity on Windows, so if I find any resolution to this I'll update the post.

For now, though, this is the result of extensive testing and a lot of assistance from others. Hopefully it helps people who (like me) require Bootcamp and are wondering why there's been such a performance drop off between 2019 and 2020. Fingers crossed there's some kind of resolution available with enough digging and testing.