The card-changeable permanent-magnet-twistor memory is a large capacity (ca 10₅ bits) storage media for information that is infrequently changed. The information is stored in the form of small bar magnets bonded to a removable plastic card. The magnets, when magnetized, inhibit the switching of a section of twistor wire at a twistor-wire-solenoid crosspoint. For maximum information density the magnet shape and strength must be optimized with respect to the magnet's action on the inhibited crosspoint and the fringing action on neighboring crosspoints. The objective is a magnet with a small dipole moment, but with adequate inhibition of the twistor switching over a reasonable range of misposition. Suitable magnet shapes and a general discussion of the stray fields in a large array of magnets are given. For maximum capacity, the transmission characteristics of the twistor wire and the character of the access switch must be considered. Two novel structures of this memory permit increased information density and capacity. The feasibility of a random-access high-density memory submodule containing 360,000 bits in 0.7 foot3 with a cycle time of 5 μsec has been demonstrated.