Hysteresis is a condition of persistence commonly affecting analog media, whereby the previous states of a system remain discernable as residual memory traces. This effect was first reported in 1947 when two new kinds of magnetic audio tapes were introduced with varying degrees of coercivity (resistance to demagnetization); it may also result from errant microns located at the edge of a recorded track which have escaped full erasure and haunt subsequent recordings. In the digital realm, the persistence of trace evidence from previous data inscriptions is known as data remanence. Although erased digital data is flagged by the system as a space that is now available for use, the actual data remains in place until such time that its space on the hard drive is actually required. This future-oriented allocation of data-space allows data that awaits its erasure to be recovered by various techniques of forensic data recovery.