Geared compressor for gas turbine engine

A booster assembly for a gas turbine engine having a first rotor assembly comprising a low pressure turbine drivingly connected to a fan via a first shaft and a second rotor assembly comprising a second turbine drivingly connected to a high pressure compressor via a second shaft, the first and second rotor assemblies arranged to undergo relative rotation in use about a common axis, the booster assembly comprising:

• a further compressor arranged to be disposed about said common axis between the fan and high-pressure compressor in a direction of flow;
• and
• a gearing having first and second input rotors and an output rotor, the first input rotor arranged to be driven by the first rotor assembly and the second input rotor arranged to be driven by the second rotor assembly such that the output rotor drives the further compressor in dependence upon the difference in rotational speed between the first and second rotor assemblies.