IBM 1360

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 (about 160 GB), a number that sounds fairly impressive even in the 2000s, and considerably more so in 1967 when it was released.

History

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. The first two, built under a $2.1 million Atomic Energy Commission grant, were installed at Lawrence Livermore in 1967 and Lawrence Berkley in 1968. Although more were ordered and delivered to the National Security Agency and Los Alamos, 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 1980. Magnetic tape, such as the tape in the IBM 3850, required stricter attention to humidity and temperature than the optical film of the Photostore. Only one similar commercial system seems to have been built, the Foto-Mem FM 390, from the late 1960s.

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, 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.

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. The cells were identical to those used in the IBM 1350 Photo Image Storage and Retrieval System. 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 4 Mbit of user data of the 6.6 Mbit 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 "tray"s (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 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 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.

The storage unit of the earlier USAF AN/GSQ-16 Computer Set, which was used for Russian to English translation, was an 10 inch optical disk IBM Photostore. It used spinning disks of Eastman Kodak's High Resolution Plate material coated on either glass or mylar.

References

G.W King, "Data Processing with the Photostore," Chap. 19 of "Large Capacity Memory Techniques for Computing Systems," The Micmillian Company, New York, 1962.

Robert J. Potter, "Component Evaluation for an Optical Data Processor," in "Optical Processing of Information," Donald K. Pollock, et al., eds., Spartan Books, Baltimore, 1963, pp. 168-186. Describes the IBM Photostore in the AN/GSQ-16.

Emerson W. Pugh, Lyle R. Johnson, John H. Palmer, "IBM's 360 and Early 370 Systems", MIT Press, 1991, pp. 280-284. Explains the 1360's relationship to IBM's Walnut and Cypress projects.

External links

* [http://www.computerhistory.org/virtualvisiblestorage/artifact_frame.php?tax_id=02.07.01.00 Photostore at computerhistory.org]
* [http://www.computer-history.info/Page4.dir/pages/Photostore.dir/PhotostoreManual.pdf Operator's Manual] (PDF)
* [http://www.research.ibm.com/journal/rd/126/ibmrd1206B.pdf Error Detection and Correction in a Photo-Digital Storage System] (PDF)
* [http://www.computer-history.info/Page4.dir/pages/Photostore.dir/index.html Photostore by John Fletcher (contains pictures and schematics)]

Note

The author of the first link 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.