I still wonder if it's true emulation ...

What else could it be? 'Cause I'm still baffled by the idea that an Xbox One can actually emulate a 360.

As time goes by, Microsoft should be able to update the 360 virtual machine to make games run better. They need to let us disable vsync so games can run faster.

From what I gathered it's part recompiled, part emulation. You have to download the game to run it, it doesn't run off the original disk.

According to DF they emulate it by splitting the 2 threads of each of the 3 XBox 360 cores over 6 XBox One cores. So assuming the dual threads on the 3.2 ghz cores are fairly balanced, it should be running nearly as well on 2 separate 1.75 ghz cores, maybe even a little better in some scenarios. The GPU is obviously a lot faster on XBox One, yet one tricky point is the 10mb of EDram on 360 which is a lot faster than the 32mb of esram (256 GB/s vs 102 in + 102 out)
So I guess a game like Viva Pinata that doesn't rely a lot on EDram or heavy graphical effects, and more on tracking many moving elements benefits from the slight increase of cpu cycles per thread.
That's all speculation though. There are many more factors. Faster HDD access with the game fully installed helps as well. Plus I guess they can even cache most of the game in RAM to speed it up even further. Most last gen games would fir comfortably in RAM and have enough left over to simulate the 512mb working memory of the 360.

True emulation it's not. It's not in any way emulating the IBM power PC 3.2 ghz cores.
It's cool that it works, a little less cool that you need to download a separate image before it works. You still need to hang on to that 360 if you want to be sure to be able to play it after the servers shut down. (Mind the servers will probably last longer than the 360...)

I see. Sounds like they're performing some technical gymnastics make this work. I thought it was wierd that you're required to redownload a game for it to run. IIRC, PC emulators like PCSX2 let you play games straight from their original discs.

I also didn't realize the the Xbox One was using ESram. All this time I thought it was ESram in the 360 and EDram in the XBOne. As I don't really know anything about the technology, I saw the bigger number and assumed EDram to be superior. Though from your post I take it ESram supports simultaneous read/write or something like that?

I don't know how often simultaneous read/write operations can be used, it sounds more like a way to make the final number sound better. 204 GB/s sounds better opposed to the 176 GB/s unified memory speed of the ps4.

Now I look into it I might be wrong about the edram from the 360. The 256 GB/s is only internal inside the memory logic (whatever that means) It seems the bandwidth to the GPU was only 32 GB/s. ESram communicates at 102 GB/s with the GPU and has the potential to go over that with simultaeneous read and write operations where possible.

From wikipedia (take it with a grain of salt I guess)
The eDRAM internal logic to its internal memory bandwidth is 256 GB/s. The high bandwidth is used primarily for z-buffering, alpha blending, and antialiasing; it saves time and space on the GPU die. Between the eDRAM die and the GPU, data is transferred at 32 GB/s.^[7] The memory interface bus has a bandwidth of 22.40 GB/s and the Southbridge a bandwidth of 500 MB/s.

So I guess games that rely heavily on those 3 operations in EDram need a bit of extra work to emulate.

The complete list of the first 100+ games hasn't been made offical yet.

I got Rare replay but I doubt I will spend much time playing Via Pinata doesn't look like my type of game. Most of my time will be spend with the Banjoo Kazooie games Conker and Touched by the Ghoulies.