So far, Raspberry Pi and Odroid C1 have been running in 32-bit mode. This is changing rapidly. Raspberry Pi 3 was introduced in the beginning of March 2016. It has 64-bit ARM-based processor onboard. You can still purchase Raspi 3 for 35 $. What a bargain! In addition, a rival Odroid C2 is also out! Five bucks more expensive Odroid C2 has 2 GB of RAM and 64-bit processor.
Why is 64-bit ARM so important? There is one well-known barrier; 4 GB of RAM which is maximum for 32-bit systems. But isn't there only 1 GB RAM in Raspi? True. However, things change. One day you might be running a laptop like NexDeck with Raspberry Pi 3 attached. You'll be needing all the power 64-bit ARM has to offer. With 2 GB or more RAM Raspberry Pi 4 or 5 can replace your existing PC.
But will that new hardware take us to the 64-bit world? No. Software is still 32-bit. I takes some time before we can download different ISO-images for older and the latest Raspi computers. Meanwhile the one and only Raspbian image there is takes care of all the hardware generations of Raspi computers. I like that. What comes to Odroid, I only own C1 which is 32-bit. However Odroid C2 will sooner or later run 64-bit Linux. No doubt about it.
Raspberry Pi 3