Type 30 to pick points on the display. An optional character generator and hardware for line and curve generation are available. Computer music MIT hackers also used the PDP-1 for playing music in four-part harmony, using some special hardware – four flip-flops directly controlled by the processor (the audio signal is filtered with simple RC filters). Music was prepared via Peter Samson's Harmony Compiler, a sophisticated text-based program with some features specifically oriented toward the efficient coding of baroque music. Several hours of music were prepared for it, including Bach fugues, all of Mozart's Eine kleine Nachtmusik, the Ode to Joy movement concluding Beethoven's Symphony No. 9, Christmas carols, and numerous popular songs. Current status Only three PDP-1 computers are still known to exist, and all three are in the collection of the Computer History Museum (CHM). One is the prototype formerly used at MIT, and the other two are production PDP-1C machines. One of the latter, serial number 55 (the last PDP-1 made) has been restored to working order, is on exhibit, and is demonstrated on two Saturdays every month. The demonstrations include: the game Spacewar! graphics demonstrations such as Snowflake playing music Software simulations of the PDP-1 exist in SIMH and MESS, hardware recreation through FPGA exists for the MiSTer project as well, and binary image paper tapes of the software exist in the bitsavers.org archives. See also History of computers History of computer science Spacewar! Tech Model Railroad Club Timeline of computing Notes External links DEC minicomputers Transistorized computers 18-bit computers Computer-related introductions in 1959 Computer-related introductions in 1960