I'm an electronics newbie.
I'm totally confused. Using Google I've tried to find out the differences between AVR architecture & ARM architecture. Google hasn't been much help. I know that I can get 32-bit AVR or 32-bit ARM.
At the base level, an 8-bit AVR, a 32-bit AVR, and a 32-bit ARM are just chips that support a particular instruction set. An instruction set is just ways to interpret the 0's and 1's in the program memory. Think of it like human languages with no translators involved. If you go to France, you must speak French to communicate effectively with people, if you go to Russia you must speak Russian. This is an analogy, just to say that at the core level, the cpus are very different.
However, most people do not interact with the machine at the core binary level, they use a compiler (GCC in this case) to convert code to the binary form used by the chips. GCC supports many different targets, you use an ARM GCC to compile code for ARM boxes, AVR 8-bit GCC for AVR 8-bit microprocessors, etc. Above the compiler is the IDE (integrated development environment) that most people use to control the compiler. Depending on the capabilities of the chip, you run a Linux environment instead of the Arduino environment.
When people talk about programming an Arduino, they could mean programming a board built by the Arduino company (Uno, Mega, etc.) or more commonly they mean using the Arduino libraries, IDE, etc. for a particular platform. The most common Arduino compatible platform is the 8-bit AVR processor using ATmega or ATtiny chips.
There are Arm chips that run the Arduino environment, including the Due by the Arduino company, the Teensy 3.0 and 3.1 by PJRC: http://www.pjrc.com/teensy/index.html
, and the DigiX by Digistump: http://digistump.com/wiki/digix
. I have the Teensy 3.0, and it runs most Arduino programs as it, due to the tireless efforts of its creator Paul Stoffregen. I also bought the DigiX during its kickstarter campaign, but so far I haven't powered it up. The Teensy 3.0 is my main platform for coding these days. As far as I know, nobody has come out with the 32-bit AVR in an Arduino platform.
If you need more computing power/memory/etc. you can go up to the Arm based Linux systems, such as the Rasberry Pi, Beagle Bone Black, pcDunio. There you tend to be further away from devices, but you often times have a bigger picture on the environment. You can combine the two, using a Linux computer for the brains, and network connectivity, and one or more boards running chips with the Arduino environment to do real time control. There are some that are combined into a single board, and others that you buy as separate units, and then interconnect them.
I want to get an Arduino but there are so many different ones that it's hard for me to choose which one. I went to the Atmel website & looked around & it didn't help answer my questions. Does Arduino use only AVR? Does Arduino have any 32-bit Atmel micro-controllers? Is ARM used in the likes of Raspberry Pi & Beaglebone?
I recommend getting an Arduino Uno to people starting out. The Uno is the default platform, and most things will run on the Uno. There is a whole cottage industry of producing shields that sit on top of the Uno to provide extra functionality. If you buy an official Arduino processor, it helps fund this site. I would recommend for starting out, get an Uno and a starter kit that has a breadboard, wires, some LEDs, some simple sensors, etc. Here is one starter kit that is made by Terry King who posts in these forums: http://yourduino.com/sunshop2/index.php?l=product_detail&p=244