The IBM 1360 Photo-Digital Storage System, or PDSS, was an online archival storage system for large data centers. It was the first storage device designed from the start to hold a terabit of data (128 GB). The 1360 stored data on index card sized pieces of stiff photographic film that were individually retrieved and read, and could be updated by copying data, with changes, to a new card. Only six PDSSs were constructed, including the prototype, and IBM abandoned the film-card system and moved on to other storage systems soon after. Only one similar commercial system seems to have been developed, the Foto-Mem FM 390, from the late 1960s. History Walnut In the mid-1950s IBM's San Jose lab was contracted by the CIA to provide a system to retrieve vast numbers of printed documents. The lab was interested in using a new type of photographic film known as Kalvar. Kalvar was developed to make copies of existing microfilm stock, simply by placing the Kalvar and original together, exposing them to ultraviolet light, and then heating the Kalvar to develop it. This could be carried out in a continuous roll-to-roll process. IBM's proposal, code named "Walnut", was a mechanical system that would automate the process of copying materials in the store using the Kalvar film. To further develop the system, in January 1958 IBM hired Jack Kuehler to head up a team exploring Kalvar-based films. He quickly concluded that Kalvar was not stable enough to store data with the sort of reliability IBM demanded, breaking down over a period of a few years and giving off corrosive gas while it did so. Kalvar is based on a diazo film and Kuehler was able to identify a similar film that would provide the reliability required, although at the price of needing to be developed in a wet lab process. He proposed a new version of Walnut that replaced the Kalvar developer with an automated diazo film developer system that developed the film in a few minutes. He was able to convince the CIA to accept this change, and the new version was announced in 1961 and delivered the next year. The primary element in a Walnut system was a large cylindrical carousel called the document store. Each store contained 200 small boxes IBM referred to as cells, in keeping with earlier magnetic tape-based systems. Each cell contained 50 strips of film, each