Is there a specific download for 64 bit Raspbian? Since Raspberry Pi 3 is 64 bit, but there is only one download for Raspbian available, is there a 64 bit version? Or, am I just confused and they found a way to intelligently determine if the Pi is 32 bit or 64 bit to install Raspbian?
There is only a single download for Raspbian, but this includes ARM6 and ARM7 kernels.
If you look at the files installed in the boot sector there is support for all models, with different internal settings.
The Pi determines at boot time, the appropriate kernel and Device Tree settings for each model.
The Pi2 and Pi3 share a common kernel, and modules.
There is no specific 64 bit support. This has been discussed, but no convincing advantage for 64 bit support seems to exist. Indeed with 1GiB of memory, it is hard to see what advantage 64 bit would provide.