which are 0.83 micrometers long and 0.5 micrometers wide, arranged in tracks spaced 1.6 micrometers apart. DVD disks are essentially a higher-density CD, using more of the disk surface, smaller pits (0.64 micrometers), and tighter tracks (0.74 micrometers), offering a density of about 2.2 Gbit/in2. Single-layer HD DVD and Blu-ray disks offer densities around 7.5 Gbit/in2 and 12.5 Gbit/in2, respectively. When introduced in 1982 CDs had considerably higher densities than hard disk drives, but hard disk drives have since advanced much more quickly and eclipsed optical media in both areal density and capacity per device. Magnetic tape media The first magnetic tape drive, the Univac Uniservo, recorded at the density of 128 bit/in on a half-inch magnetic tape, resulting in the areal density of 256 bit/in2. In 2015, IBM and Fujifilm claimed a new record for the magnetic tape areal density of 123 Gbit/in2, while LTO-6, the highest-density production tape shipping in 2015, provides an areal density of 0.84 Gbit/in2. Research A number of technologies are attempting to surpass the densities of existing media. IBM aimed to commercialize their Millipede memory system at 1 Tbit/in2 in 2007 but development appears to be moribund. A newer IBM technology, racetrack memory, uses an array of many small nanoscopic wires arranged in 3D, each holding numerous bits to improve density. Although exact numbers have not been mentioned, IBM news articles talk of "100 times" increases. Holographic storage technologies are also attempting to leapfrog existing systems, but they too have been losing the race, and are estimated to offer 1 Tbit/in2 as well, with about 250 GB/in2 being the best demonstrated to date for non-quantum holography systems. Other experimental technologies offer even higher densities. Molecular polymer storage has been shown to store 10 Tbit/in2. By far the densest type of memory storage experimentally to date is electronic quantum holography. By superimposing images of different wavelengths into the same hologram, in 2009 a Stanford research team achieved a bit density of 35 bit/electron (approximately 3 exabytes/in2) using electron microscopes and a copper medium. In 2012, DNA was successfully used as an experimental data storage medium, but required a DNA synthesizer and DNA microchips for the transcoding. , DNA holds the record for highest-density storage medium. In March 2017, scientists at Columbia University and the New York Genome Center published a method known as DNA Fountain which allows perfect retrieval of information from a density of