The 5,000 programming steps were addressed with a letters from A-E and three decimal digits e.g. B253. The letter was decided in various ways, one example was by a decision (e.g. whether some information was present, e.g. A=true, B=false resulting in either A253 or B253). Each named step consisted of eight decimal digits, depending on which cores the wire was threaded through. The first three digits (e.g. 891) told the MCU what program step to go to next. The next two digits defined the operation (e.g. 55, compare two pieces of information) and the last three told the MCU where to store the result (e.g. 020, put this information in Main Ferrite Store 10). So the whole program step would be 89155020 which would lead to the next step being A891 if the answer was true or B891 if the answer was false. Each step took 12 microseconds to execute. The program could be easily changed, on site, as developments and upgrades occurred throughout the life of the TXE4 design.