Data storage is one area of technology where nanotechnology has been used even before the term nanotechnology became very popular. The magnetic recording media — the disk that stores information in hard disk drives — used nanotechnology in the late 1990s, in the form of grains which are 15 nm or less in diameter (the grains in current technology are about 8 nm in diameter). The reading sensors of hard disk also make use of thin nanostructures in several dimensions to read information from the recording media. This paper introduces the technology behind the magnetic random access memory and related topics, which form the core of the symposium L of ICMAT 2011, which is titled "Memory, Nanomagnetics, Materials and Devices".