The Esdac Film (1951, 1976)

# EDSAC Film (1951, 1976): Documenting the First Film Showing a Stored-Program Computer in Operation **TL;DR**: This film is a documentary produced for the first Joint Computer Conference in 1951, showcasing the workflow of the EDSAC computer. It is widely recognized as the first film documenting a stored-program computer in operation. ## Background and Purpose of the Film The film was produced around December 1951 for the first Joint Computer Conference held in Philadelphia. The EDSAC computer had been operational since May 1949, and the team had developed a programming system based on a library of subroutines at that time. The film aimed to demonstrate the operation of EDSAC to its audience, telling a complete programming story. ## Plot and Characters of the Film The film tells a story "like a good American movie." All roles were played by members of the laboratory: - **Sandy Douglas** portrays a mathematician. - **Stanley Gill** plays the programmer. - **Eric Mackey** (briefly appearing) serves as the director. - **Margaret Harrie** (the narrator's secretary) handles program punching. The story begins with the mathematician explaining a problem to an expert committee. The committee discusses solutions, focusing on which subroutines to select from the library. Subroutines are a recurring theme throughout the film, with the narrator noting that this film "could almost be seen as a commercial for subroutines." The problem is then handed over to the programmer, who checks, punches the program onto paper tape, and finally runs it on the computer. ## EDSAC Technical Details The film includes several shots showcasing the hardware and operational state of EDSAC: - **Memory**: Uses a serial ultrasonic delay-line memory, consisting of 32 "tanks," each capable of storing 16 words. - **Memory Monitor**: The stored content can be displayed on a cathode-ray tube, with 16 lines, each corresponding to a word. Binary "1" is represented by a bright spot, and "0" by no spot. - **Instruction Input**: The film shows the process of reading in program tapes, with instructions filling a "tank" from bottom to top. Each instruction consists of several characters, punched as a row of holes on paper tape, read by the initial input program, and assembled into binary form, including the conversion from decimal addresses to binary. - **Other Components**: Shots include memory tanks within a temperature-controlled enclosure, vacuum tube panels, wiring behind the panels, and overhead views. ## Programming and Execution Process The film details the specific steps of programming and execution at that time: 1. **Programming Preparation**: The programmer consults the subroutine catalog based on the problem's requirements to determine the necessary subroutines (e.g., integration, exponential function, tape reading, and printing subroutines). 2. **Punching and Verification**: Secretary Margaret Harrie punches the program onto paper tape. The standard practice (though not always followed) was to punch twice and then use a comparator machine to mechanically compare the two tapes to ensure accuracy. 3. **Submission for Execution**: The verified tapes were labeled and placed in the processing queue. 4. **Computation Process**: While EDSAC runs other programs, the operator inserts the new program tape into the photoelectric paper tape reader. Instructions are read into memory, and the numbers in memory change as the computation progresses. 5. **Debugging**: If the results are incorrect, a tracing program is used for debugging, which prints the functional letter of each instruction as it is executed. ## Significance of the Film The narrator points out that this should be the first film showing a stored-program computer in operation. The film not only documents the operation of EDSAC but also reflects the actual workflow of computer programming in the early 1950s, particularly the use of subroutine libraries. This old film aims to give audiences an intuitive understanding of computer operations in 1951. Source: https://www.youtube.com/watch?v=DjhRRj6WYcs