IBM 1360
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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, a number that sounds fairly impressive even today, and considerably more so in 1967 when it was released.
Developed in the mid-1960s at IBM's San Jose, California storage research labs (home of the first hard drives and many other advances), the 1360 was the ultimate development of the Cypress and Walnut projects that took place over the better part of the decade. Only six photostores were built in total. Although more were ordered, IBM soon introduced similar but much less complex systems such as the IBM 3850 that took over its role. Nevertheless its few users generally hated to see them go when IBM decided to end support for the devices in the 1980s.
Data was stored on small 2.75 x 1.377 inch cards of stiff film known as chips, each one holding 32 data "fields" in a 4 x 8 array. Each field contained 300 lines of data of 300 bits each, 0's written as a black-clear pattern, and 1's as a clear-black (using Manchester encoding). In total each chip held about 6.6 Mbits.
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."
New chips were delivered in plastic boxes known as cells, each holding 32 chips. Cells were in turn delivered in boxes of ten, wrapped in a lightproof wrapper. 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 most camera shops today; 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 storage capacity – thus each chip held just over 4Mb of user data of the 6.6Mb available. 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. Non-working chips were automatically discarded and another one made to replace it, while the data was still in memory.
Once processed, the chips were re-inserted into the cell they were removed from earlier. They were then moved out of the reader and into the 1351 Cell File & Control or additional storage-only 1362 Cell File units. 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 1362 for a total of one terabit, but other installations typically had two more 1362'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 vacuum 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 system was a small computer, programmed similarly to industrial control systems with a fixed number of tasks running all the time. The controller was also tasked with translating the data to and from the host format. IBM surprisingly offered the 1367 Data Controller for Control Data systems, realizing that most users with this sort of storage need had a number of CDC machines. Other Controllers were available for different host platforms.
[edit] Note
The author of the first link below notes that the LLNL Photostore was filled thirteen times over before being retired. The software would call for cells to be re-inserted on demand from storage.
