Experiments to study plasma formation and implosion dynamics of wire array z pinches performed on MAGPIE generator (1.4 MA, 240 ns) at Imperial College are reviewed. Data from laser probing and X-ray radiography show that heterogeneous plasma structure with dense wire cores surrounded by low-density coronal plasma persists in wire arrays for a significant part of the implosion. Early implosion of the coronal plasma produces a precursor plasma column on the array axis, parameters of which depend on the rate of radiative cooling. The seeding of perturbations on the dense core of each wire is provided by nonuniform sweeping of the low-density coronal plasma from the cores by the global J × B force. The spatial scale of these perturbations (∼0.5 mm for Al, ∼0.25 mm for W) is determined by the size of the wire cores (∼0.25 mm for Al, ∼0.1 mm for W). A qualitative change in implosion dynamics, with transition to 0-D-like trajectory, was observed in Al arrays when the ratio of interwire gap to wire core size was decreased to ∼3. In experiments with nested wire arrays, two different modes of operation were identified, both giving significant sharpening of the X-ray pulse (∼10 ns) in comparison with a single array, despite the small number of wires in the arrays (16 outer, 16 inner) and the long implosion time (260 ns).