Large-scale computer data storage. View of a library store of data storage tape cartridges. Each cartridge uses a plastic tape coated in chromium dioxide to store the digital data magnetically. There are 18 tracks running parallel along the length of each tape, giving a maximum storage capacity of 200 megabytes (Mb). This library, at the US National Centre for Atmospheric Research, holds over 100,000 cartridges containing data used in global climate modelling. The total volume of data is equivalent to 200 billion pages of typed information. New equipment installed in 1991 enables data recording at twice the previous density (ie 400 Mb per cartridge).