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PDP15 System Development: 1973
The Graphics Section for most of 1973 consisted of Eric Thomas in charge of Alan Francis, Julian Gallop, Wade Shaw and David Toll. Julian and Wade worked predominantly on the PDP15 while David and Eric were mainly involved with the 1906A software. Alan Francis worked on both the 1906A, the PDP15 (in particular the VCS3 synthesiser) and the SD 4020.
By 1973, quite a bit of software had been developed and DEC systems modified that it was nearly a full time job just maintaining the software available. The arrival of the 1906A had brought magnetic tapes, paper tape etc all with different formats that required systems effort to allow them to be used on the PDP15. The original operating systems on the PDP15 was being replaced by RXS Plus. The hardware was also beginning to need maintenance. Resistors were burning out. The spark pen for the writing tablet wore out every 40 hours of use. The pushbuttons on the VT15 became unreliable and had to be replaced several times. The spark pen caused characters from the keyboard to be misread when it was close to the keyboard. Several shielding techniques were tried without success. The only real solution was to move the tablet/spark pen 4 feet away from the display that this required an operator with very long arms!
The memory on the machine was upgraded for a second time to bring the memory up to 64 Kwords. The cycle time for the new store was slower (980nanosecs compared with 800 nanosecs) but much cheaper. The new memory could not be addressed directly but was accessible via an index register. Two more discs were added to bring the total size up to 1 Mwords.
A Tektronix storage tube was added to the system via the teletype interface.