You people really need to stop doing things like this. My girlfriend thinks I'm nuts when I start laughing out loud at my laptop.

edit: I totally forgot to chime in on the OP's question. A1 is aluminum, I'm not sure if it's 6000 or 7000 series (pretty sure it's 6000) while the M4 is Specialized's "metal matrix" special blend. It's aluminum, but apparently, it also has aluminum oxide particles as an additive in the tubing material. This is supposed to increase stiffness while reducing weight, although I've never compared weights, I've ridden frames made with both, and never really noticed any real noticeable difference.