[Nexus 9 Q&A, Help & Troubleshooting] therealzam:
People like to blame the 64bit OS because the switch does make processes consume slightly more memory. If implemented poorly, a 64bit OS can eat up a lot more RAM. Windows XP 64, any Itanium based system and many early x64 Linux distributions come to mind.

Somehow Android OS on my N6 averages 220mb, while it's 800+ on the N9. Because the N9 is 64 bit, that change seems to be the obvious culprit. Clearly, the N9 didn't ship with enough RAM based on the OS memory use as somehow the N6 has 3gb for an 220MB OS footprint and the N9 has only 2mb, despite an OS that eats almost 4x the memory.

Switching to a 64bit OS should make the CPU, RAM, etc. all run 'faster', but if there's not enough RAM to hold running software, the experience will slow down as more processes need to be shuffled in and out of RAM. Look at what happens to a computer when it 'runs out of RAM'. The constant game of musical RAM chairs will more than erase any gains from switching to 64 bit.

In my mind, there is no question that SERIOUS problems exist with this device. The fact that this is one of the first 64bit Android devices is almost definitely a contributing factor, but the slightly reduced efficiency of how 64bit memory is allocated can in no way explain the problems with the devices. Something MUCH deeper is going on. Based on some research, here is what I've learned.

1: Some part of the OS is using an obscene amount of memory. Some of this is probably Google's fault because 64 bit Android just wasn't ready. I'm also pretty sure nVidia and HTC are more to blame for this issue than Google.

2: There's still not enough RAM. If the N6 has 3GB, there is no reason why the N9 shouldn't. Most tablet users run more memory-intensive

3: HTC built a bad device. I've had cellular issues with VZW & ATT which have been discussed in these forums and are obviously HTC's fault. I've also read about there being some hardware issues causing the ram to 'freeze' which required a replacement device.

4: nVidia's hardware sucks. More accurately, their x64 bit implementation of the hardware.

5: Graphics: I BELIEVE THIS IS THE GIANT ELEPHANT IN THE ROOM OF ISSUES. The nVidia Shield has similar hardware with a standard HD screen. The N9 has a different aspect ratio and a lot more pixels. The horrible application switching lag even with relatively low memory use (a process that is still taxing on the GPU) makes me think this is the main flaw of the device. This problem could also make the OS eat more memory to make up for the OS issues. A graphics issue would be everyone's fault. Google is to blame for insisting on this change when the other hardware just couldn't support it properly and choosing partners incapable of delivering the hardware to properly support the screen. nVidia and HTC to blame for not providing sufficient hardware and software support for the screen.

In reality, I think several factors combined to produce this issue. The components of the system were designed primarily for 32-bit implementations of Android. 64-bit support was baked into them, but it wasn't the focus of the components. The device itself was probably designed before 64-bit Android was even available to test properly. Because the pieces looked like they should fit together on paper, everyone just assumed they would. Unfortunately,for some components the fact that they could run in 64-bit mode, didn't mean they would run well.