Personally I believe in documenting things, because an undocumented feature may as well not exist.
Here is some Arduino stuff I documented:http://www.gammon.com.au/forum/?bbtopic_id=123
Do different Arduino's have different USB host capabilities? I
Yes, they do have different USB
capabilities. The ones which have the "U" version of the chips are more capable in that respect, for example the Leonardo with the ATmega32u4 chip. This can certainly be (easily) used as a USB slave, in fact I have one here mimicking a keyboard, but you can also mimic a mouse, joystick etc.
The ones which do not have the USB capability can to an extent do the same thing, albeit fairly slowly and with fairly critical timing loops.
A search for "leonardo arduino usb host" revealed this thread: http://arduino.cc/forum/index.php?topic=108994.0
The suggestion there is that the ATmega32u4 chip can be a slave and not a host.
You may find the Products page (http://arduino.cc/en/Main/Products
) helpful (to an extent) although I'm not sure how much detail they give about each board.
If the Arduino and its shields was a Microsoft or Oracle product all of this would be fully documented
Yes, well perhaps. But you pay for that documentation, and in the case of the companies mentioned, I would suggest quite a lot.
The thing is, most (almost all) shields are independently produced, so there is no one organization you can line up and criticize for not documenting things.
If I went to a car (automobile) dealer there would be no problem getting an overview of what all the models could do ...
Perhaps, again. But if I went to a car dealer I would expect to have to answer questions. Eg. Do you want to carry a lot of luggage? Travel quickly? Carry heavy loads? Have long range? Be cheap? Be safe? Carry 8 passengers?
The answers then guide the information which is given to you.
Just curious, why this fascination with USB host shields? There is another thread where someone regularly asks for multi-threading without ever explaining why he needs it or what his project is. It is like he has heard multi-threading is a great idea and is trying to find a use for it.
I got 80,000 hits on a Google search for "arduino usb host shield". Since I don't personally have a use for one right now, you
may as well read those and see what you find, rather than one of us doing it and repeating whatever-it-is that those pages say.