


The proofofconcept machine functionally consisted of two 25bit registers, a 1bit carry register and a 1bitwide arithmetic unit capable of addition and subtraction.
The registers were implemented using capacitors, one per bit, arranged radially on a revolving disc. Stationary contacts sensed the stored charge on the capacitors. These signals were sent through the electronics, and thence back to another contact to refresh or update the charge. Note this is the same principle (periodic refreshing of capacitive charge) employed today in dynamic RAM chips.
The arithmetic unit, or AddSubtract Mechanism as it was called, was constructed with vacuum tubes and employed the principles of binary arithmetic, not counters. Addition and subtraction were performed in a bitserial fashion with the 1bit carry register holding the carry state from the processing of one bit till the next.
According to the diagram in the book "The First Electronic Computer", there were no input/output facilities on this machine. One can speculate that input may have been performed by briefly connecting appropriate points on the machine so as to insert a random number into the registers. Output may have been viewed on an external oscilloscope. After recording the injected random values as viewed on the scope, an arithmetic operation could be performed, and the result checked by again viewing the scope.
Nothing remains of the original proofofconcept machine. In the early 1970s Atanasoff recreated some diagrams and a reconstruction was built for the ENIAC court case over patent rights to the concept of digital electronic computing.


ProofofConcept
 Architecture
 ASM
 Manual
 Simulation
ABC 
bhilpert 2002 