Variable displacement pumps are a key component to a variety of mobile and industrial hydraulic systems, yet the efficiency of existing pump architectures is poor at low displacement. As a solution to this issue, a new pump architecture is proposed that eliminates the planar hydrodynamic joints of a conventional architecture with rolling-element pin joints in an adjustable linkage. This new architecture uses an adjustable six-bar linkage that reaches true zero displacement and has the same top-dead-center (TDC) position regardless of displacement. In this work, the linkage kinematics and dynamics are discussed, an energy loss model is developed and used to drive design decisions of a first generation prototype, and experimental results are presented to validate the model. It is shown that this linkage-based, variable, positive displacement architecture shows promise as a highly efficient alternative to existing pump architectures across a wide range of displacements.