The S10 is one of the latest creations from Microsoft (at the time of writing) and is (so far) my favourite of those in my collection. It's on the borderline of being classed as "miniature" in my collection; i.e. if I put it on the shelf along with the other miniatures, the wood base just overhangs the shelf. (The cast base of the engine itself would fit easily.)
It's a single cylinder "mill" type engine with no boiler and including a working governor. It is made mainly in brass with some small stainless steel parts.
The cylinder is a double acting type with a piston valve (I think); approx 15mm bore x 20mm stroke. The piston rod and connecting rod are joined with a proper crosshead, sliding between two pairs of parallel bars. The crankshaft has a simple counterbalanced crank at one end and a 55mm diameter cast brass spoked flywheel at the other end. In between the main bearings there is an eccentric controlling the valve rod. The valve appears to be a "piston" type but I'm not sure about that. There could conceivably be a small D slide valve inside the chest.
The steam inlet is controlled by a rotary valve operated, via a pair of universal joints, by a real working flyball governor. This is unusual in an engine of this size. The governor is driven by a belt from a pulley on the flywheel. Both inlet and exhaust have small compression fittings.
The various parts of the engine are bolted to a cast brass bed, which is, itself, mounted on a nice wooden base measuring 180mm x 100mm.