High Definition CD or HDCD - What is it exactly?

I have an Audio Aero Capitole MKII and always thought it had the ability to read HDCD's. I thought this until recently playing an HDCD on a friend's CEC CD player which has a small light that appears that tells you that it is reading the disc as an HDCD. The improvement and realism in the sound was awesome. The realism in sound reminded me of SACD in many ways, although I don't have much listening experience with either HDCD or SACD.

What exactly is HDCD and why can't the Aero Aero (at this price point) play/read these types of CD's?

One more thing...I burned a copy of the HDCD, but the CEC player did not recognize the copy as an HDCD.

Your comments are appreciated. Thanks,