a Capillary electrophoresis demonstrating elongation of stack complexes as signals X, Y, then X are recorded (lanes 2–5), followed by truncation of stack complexes during popping (lanes 6–8). Black circled numbers denote the target number of signals recorded in each lane. Blue arrows on virtual gel image denote migration band of target stack complex in each lane. b Conversion of capillary migration time ladder in seconds to approximate base pairs. c, d Recording signals on the stack data structure (lanes 2–5) and then analysis of only supernatant solution after read operations (lanes 6–8) revealing the double stranded signal complexes Xr and Yr popped off stacks. c X, X then Y is recorded, resulting in complexes Yr, Xr then Xr being popped into supernatant in reverse order. d Y, X then X is recorded, resulting in complexes Xr, Xr then Yr being popped. Lane reaction sequences in Supplementary Note 3.2. e Capillary electrophoresis of a stack sample where stacks are assembled with three X signals. f AFM micrograph of sample in e, scale bar 200 nm. g Distribution of stack assembly lengths on AFM micrograph (data from manual curation of 1022 objects in AFM field) showing discrete peaks at lengths corresponding to 2–7 signals. See Supplementary Note 6 for AFM of recording XYX and XXY. All experiments were repeated independently three times.