The two models of Porsche's uncompromisingly sporty 911 Carrera are each available with a steel coupe roof, or a folding convertible top, or a third variation called a Targa. A small percentage of Porsche buyers have preferred this body style since it was offered on the first generation of the 911, and this current evolution carries over those attributes: It features the security of a hardtop, but with the environmental stimulation of a convertible.

The latest Targa top was introduced for 2007 as the second generation of the motorized, retractable glass roof concept that Porsche created for Targa fans. (The name comes from an Italian road race called the Targa Florio to commemorate the company's wins there.) The glass roof is made of two sheets of tempered glass with a plastic film sandwiched between them for strength, and it opens much wider than a conventional sunroof. The glass roof sits flush against a large rear window, which opens like a large hatchback and makes it easy to load the rear seat area of the car.

The open-air environment is close to a true 911 convertible experience, yet it also offers a new thrill of driving in a closed glass cockpit – think of a jet fighter canopy. Targa roof 911s are easier to spot, too, with a polished aluminum trim piece following the line of the roof pillar on the body side.

Historically, Targa-roof Porsche 911s have come in base models only, but the latest versions are now built on the reinforced chassis of the Carrera 4 and Carrera 4S models, which have permanent all-wheel drive plus wider rear bodywork to cover wider wheels and tires. Porsche chose this configuration because the Carrera 4 and 4S offer more capability in adverse conditions than the rear-drive 911 Carrera models, in the same vein as the added capability of the Targa roof over the conventional convertible top.

Like the 911 Carrera and 911 Carrera S, the Targa models come with either of two engines, a 345-hp 3.6-liter flat six-cylinder in the Targa 4 (MSRP $92,100) and a 385-hp 3.8-liter in the Targa 4S (MSRP $103,100). Both engines come mated to six-speed manual transmissions. Optional is Porsche's twin-clutch seven-speed automatically shifting manual gearbox. The bigger motor version also gets larger wheels and tires, larger brakes and automatically adjusting shocks as standard equipment, although these items are optional on the Targa 4. Acceleration is immediate, and Porsche claims, conservatively, that the 911 Targa 4 will reach 60 mph in 5.0 seconds while the Targa 4S will get to 60 mph in just 4.5 seconds. Like the Carrera S, the Targa 4S is capable of a top speed of over 180 mph.

The suspensions of the Targa models are tuned slightly differently than their corresponding steel-roof counterparts. Both Targas use the same, larger-diameter front anti-rollbar of the Carrera 4S, as well as larger rear anti-rollbars and new jounce bumpers to control the extra weight of the glass roof. The springs are also slightly softer than those in the hardtop 911s to keep the ride smooth and supple. The actively adjusting shock absorbers have also been specially tuned for the Targa models to compensate for the different suspension calibrations.

Both Targa models are available with Porsche's composite ceramic brake system, which substantially reduces the unsprung weight on the wheel assembly for better traction at maximum speeds, which the Targa models have been engineered to handle.

On the road, the Targas are as exciting to drive as any of the 2010 Porsche 911 Carrera models, yet the glass-roof cars offer this thrill with an extra dose of ambient light and atmosphere mixed in.