and started suggesting the IBM 3850 in favor of the 1360. Magnetic tape, such as the tape in the 3850, required stricter attention to humidity and temperature than the optical film of the Photostore. Its few users generally preferred the 1360, and three of the five were still being used in 1977, and the last system shut down only in 1980 when IBM stopped servicing them. The IBM 1350 never sold a single unit. In 1966 the company started a "controlled marketing program", but after a year they realized that the system would need additional development before it would be commercially acceptable. Instead they decided to cancel its development. Description From the IBM 1360 Photo-Digital Storage System Principles of Operation Data was stored on small 35 by 70 mm cards of stiff film known as chips, each one holding 32 data "frames" in a 4 x 8 array. Each frame contained 492 lines of about 420 bits each, 0s written as a black-clear pattern, and 1s as a clear-black (using Manchester encoding). In total each chip held about 6.6 megabits. Chips were delivered in plastic boxes known as cells, each holding 32 chips. For delivery, ten cells were stacked, wrapped in a lightproof plastic wrapper, and then placed in a box. Boxes of cells were loaded into a hopper on the 1365 Photo-Digital Recorder unit, which would cut off the wrapper and drop the cells into a queue. When a cell reached the head of the queue it was removed and opened, chips being pulled out one at a time as needed. Data was written to the chips using an electron gun, similar to the operation of a television tube. Sensors and magnets on either side of the chip holder automatically focused the beam and corrected for focus as the filament wore down through use. The gun had eight filaments instead of one, automatically rotating a new one into position as needed to allow it to work for extended periods before replacement. After the chip had been written it was moved to an automated photo processing system similar to those found at camera shops; the chip was dipped into a series of liquid-filled stations to develop, and then pulled out to dry. Flaws on the film, impossible to avoid, were addressed to some degree through the use of complex error correction codes, which used up about 30% of the overall