Hard drives store data in the magnetic polarization of small patches of the surface coating on a (normally) metal disk. The maximum areal density is defined by the size of the magnetic particles in the surface, as well as the size of the "head" used to read and write the data. The areal density of disk storage devices has increased dramatically since IBM introduced the RAMAC, the first hard disk in 1956. RAMAC had an areal density of 2,000 bit/in². Commercial hard drives in 2005 typically offer densities between 100 and 150 Gbit/in², an increase of about 75 million times over the RAMAC. In 2005 Toshiba introduced a new hard drive using perpendicular recording, which features a density of 179 Gbit/in².[1] Toshiba's experimental systems have demonstrated 277 Gbit/in², and in 2006 Seagate Technology demonstrated a drive with a 421 Gbit/in² density.[2] It is expected that perpendicular recording technology can scale to about 1 Tbit/in² at its maximum. [3] Compact Discs (CDs), another common storage media of the early 2000s, stores data in small pits in plastic surface that is then covered with a thin layer of reflective metal. The standard defines pits that are 0.83 micrometers long and 0.5 micrometers wide, arranged in tracks spaced 1.6 micrometers apart, offering a density of about 0.90 Gbit/in². DVD disks are essentially a "product improved" 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. Further improvements in HD DVD and Blu-ray offer densities around 7.5 Gbit/in² and 12.5 Gbit/in², respectively (for single-layer devices in both cases). When CDs were first introduced they had considerably higher densities (and overall capacity) than then-current hard drives, however hard drives have improved much more quickly than optical media, and by the time the latest blue-laser systems become widely available in 2007, the average hard drive will store somewhere between 500 and 750 GB with densities between 150 and 250 Gbit/in². A number of technologies are attempting to surpass the densities of all of these media. IBM's Millipede memory is attempting to commercialize a system at 1 Tbit/in² in 2007 (800 Gbit/in² was demonstrated in 2005). This is about the same capacity that perpendicular hard drives are expected to "top out" at, and Millipede technology has so-far been losing the density race with hard drives. Development since mid-2006 appears to be moribund, although the latest demonstrator with 2.7 Tbit/in² seemed promising. 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. Various 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. Finally, molecular polymer storage has been shown to store 10 Tbit/in².[4] 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, a Stanford research team was able to achieve a bit density of 35bit/electron (approximately 3 Exabytes/in^2.) This was demonstrated using electron microscopes and a copper medium as reported in the Stanford Report on January 28, 2009.[5]