Difference between a variable vane turbo and non variable vane turbo?

Vanes inside a turbocharger control the acceleration of gases inside the turbo and thus the speed at which the turbocharger itself can accelerate the compressor and produce boost. Tight vanes produce a quick spooling turbo with little lag but one that can quickly choke the engine at higher speeds. This is because the engine is trying to push to much exhaust through the turbo and the vanes are constricting it. Wider spaced vanes can allow a turbo to have more top end capability but at the expense of spool time (otherwise known as turbo lag).

With a variable vane turbo the vanes themselves can be adjusted on the fly allowing the turbo to spool quickly and still be able to produce good efficiency at higher engine speeds. The technology has been about for a few years in diesel engines but has been slow in coming to gasoline engines due to increased exhaust temperatures found in gasoline engines. These increased temperatures cause lower rates of reliability. The technology has been used in gasoline engines most recently in the 2006-2007 Porsche 911.