Electrical devices whose principle of operation is based upon the use and properties of ferrites, which are magnetic oxides. Ferrite devices are divided into two categories, depending on whether the ferrite is magnetically soft (low coercivity) or hard (high coercivity). Soft ferrites are used primarily as transformers, inductors, and recording heads, and in microwave devices. Since the electrical resistivity of soft ferrites is typically 10⁶–10¹¹ times that of metals, ferrite components have much lower eddy current losses and hence are used at frequencies generally above about 10 kHz. Hard ferrites are used in permanent-magnet motors, loudspeakers, and holding devices, and as storage media in magnetic recording devices. In this article, discussion of hard ferrites will be restricted to recording only. One type of soft ferrite, referred to as square-loop ferrites, was once deployed in huge quantities as cores for digital computer memories but has now been replaced by semiconductor integrated circuits.