storage capacity – thus in each line in a frame only 300 bits were user data, the remainder being used for data redundancy. This resulted in about 4.7 Mbit of usable space in a 6.6 Mbit chip. Error correction could correct for minor imperfections, but not for larger problems or bad developing, so after developing the chips were immediately passed to the 1364 Photo-Digital Reader to ensure they worked. A non-working chip was automatically discarded and another one made to replace it while the data was still in memory. Data was read off the card by moving it in front of a fixed photocell. Access time was improved by laying out the data in rows that were read in both directions. The head would read off a track of data as the card moved from right to left (say), and then reverse direction and read the other side of the same track from left to right. Once it returned to its original position it would move onto the next track in the field. The term for this method of data access is boustrophedonic, from a Greek root meaning "as the ox plows." Many computer printers use the same technique to avoid delays moving the print head back across the paper. Once processed, the chips were re-inserted into the cell they had been removed from earlier. They were then moved out of the reader and into the 1361 Cell File & Control or additional storage-only 1352 Cell File units. Note the numbering; these units were intended to be shared with the 1350 system. Each file contained 75 trays (5x5 x 3 deep) holding 30 cells each, for a total of 2,250 cells, containing 1/2 a terabit. The system installed at LLNL used one 1361 and one 1352 for a total of one terabit, but other installations typically had two more 1352's for a total of 2 terabits. Cells could be manually moved about by loading them into the front-and-bottom-most set of trays, which could be removed. Speed of the system was fairly good, writing at about 500 kbit/s, and reading at about 2.5 Mbit/s. Cells were moved between the Files and Readers using a pneumatic tube system similar to those used to move documents around in some stores and hospitals. The system could keep up to 13 cells "in flight" around the system in order to minimize delays. Controlling the entire