The PDP-9 computer was the successor to the PDP-1, PDP-4 and PDP-7 line of 18 bit computers manufactured by Digital Equipment. There were only 445 PDP-9 machines manufactured. The PDP-9 has as standard 8192 word of 1 us cycle time core memory. Memory is expandable to 32768 words. The PDP-9 is microcoded. It has a ROPE memory that has 64 locations. Each location is 36 bits wide. The microcode even include a very simple bootstrap to read directly from paper tape with a single press of a key on the frontpanel. It uses a single accumulator register for all operations. There is also a MultiplierQuotient (MQ) register used to implement multiply and divide. The entire machine is utilizing discrete components mounted on small boards, either single width or dual width.
Our PDP-9 has been used at Studsvik nuclear testing facility in Sweden. After Studsvik our machine ended up in a high school were we got it in the 80ies. From the very comprehensive list of DEC 18 bit systems installed we get the original delivery. The serial number is 183 as seen from this badge on the system rack.
What we can get is that the first delivery was made in march 1968 when the basic processor, KC09 (central processor), KD09 (I/O logic) and MC70 (8 kword memory), paper tape reader / punch (PC09), Input/output buffer DA09, Output relay buffer DR09A, 12 bit A/D converter (AF01) and one D/A converter (AA01).
A few months later the KE09A option was added. KE09A is the extended arithmetic option that allow for faster maths operations. The KE09A options is just 45 more modules added top the backplane. In 1969 the system was upgraded with a two DEC tape units (TU55) and a DecTape controller (TC02). The same year another D/A converter was added. In 1970 two more D/A converters (AA01A) were added. In 1972 a major upgrade took place where the memory was increased from 8192 words to 16384 words (MC70). To handle this the Memory extension option was needed which was equipped with the KG09A modules.
After it has been in use at AB Atomenergi it ended up in a school in Hudiksvall. We got the computer from them in the middle of 1980ies. At that time it consisted of the main CPU, one memory cabinet, the A/D and D/A cabinet and a Cabinet which held the two TU55 drives and the TC02 controller. Directly after acquiring this machine we managed to run some test programs to exercise the CPU and memory successfully. Unfortunately we never managed to make the TC02 and TU55 drives work as supposed. We could have the software move them back and forth but there were no data read into memory.
A close up to the right. A very impressing looking front panel.
project has been started to read TU55 tapes using a micro controller based solution.
The A/D converter is a special module located in a separate chassis. This is the frontpanel.
At Rhode Island Computer Museum they also have a PDP-9 which they are working on to restore. RICM PDP-9