Non-volatile memories based on scanning probes offer very high data densities, but existing approaches require the probe to be heated, which increases the energy expenditure and complexity of fabrication. Here, we demonstrate the writing, reading and erasure of an ultrahigh-density array of nanoscopic indentations without heating either the scanning probe tip or the substrate. An atomic force microscope tip causes microphase transitions of the polystyrene-block-poly(n-pentyl methacrylate) of a block copolymer to occur at room temperature by application of pressure alone. We demonstrate a data storage density of 1 Tb in(-2), which is limited only by the size of the tip. This demonstration of a pressure-based phase-change memory at room temperature may expedite the development of next-generation ultrahigh-density data storage media.