The primary difference between CCD or 'charge coupled device' and CMOS or 'complementary metal oxide semiconductor' resides in the location where the collected light signal of photons captured by the sensor cell is converted from 'electric charge' to 'analog voltage level and then digital' signal.
In CCD type sensors the cell charge is 'shifted out' in a 'bucket brigade' to a 'charge-to-voltage-to-digital' signal converter. There are few of the converters to MANY sensor cells, and these represent somewhat of a processing bottleneck. On the other hand, much of the area of the sensor cell can be devoted to the photon collecting function.
In CMOS type sensors, the cell charge is converted to a digital signal right at the spot, but that requires more of the device area be devoted to 'charge-to-voltage-to-digital' conversion circuitry, leaving less to absorbing photons. This sensor type does not 'shift out' the charge in a 'bucket brigade' but passes the digital electronic signal out in a fashion not unlike RAM memory.
This may be a bit of an oversimplification, but either technology has its pros and cons.
p.s.: I just found the URL for a good, short article I knew I had in my 'dayfile' but could not locate before I wrote the above comment. The reference is a PDF:
If I'm not mistaken, CMOS requires significantly less power than CCD sensors. CCD's took a lead in resolution and image quality early in digital camera development and they still dominate, but Canon's CMOS sensor has essentially closed that resolution and quality gap. For now, there are a handful of CCD sensor producers for digital cameras, but Canon is alone in having a high res, high quality CMOS sensor although Foveon is working on a CMOS X3 product: