1. "The Z3 was built with 2,600 relays, implementing a 22-bit word length that operated at a clock frequency of about 5-10 Hz. Program code was stored on punched film." (Wikipedia: Z3, 7.1.23 UTC 15:10)
2. "The Z3, like its predecessors, stored its program on an external punched tape, thus no rewiring was necessary to change programs." (Wikipedia: Z3, 7.1.23 UTC 15:10)
3. "The Z3 operated as a stack machine with a stack of two registers, R1 and R2. The first load operation in a program would load the contents of a memory location in to R1; the next load operation would load the contents of a memory location into R2. Arithmetic instructions would operate on the contents of R1 and R2, leaving the result in R1, and clearing R2; the next load operation would load into R2." (Wikipedia: Z3, 7.1.23 UTC 15:10)
