Hi I'm sure it was mostly related to keeping the voltage low and still being able to get enough gain from transistors. As I recall DTL stacked at least 2 transistor plus a diode drop. More voltage and it would have used more power. Less voltage and it would have been too slow. In the DTL days, unlike today, the major factor in speed was the transistors them selves and not the interconnect. Today, the interconnect dominates and the smaller one can make the transistors, the shorter the interconnects. Dwight _________________________________________________________________ Put your friends on the big screen with Windows Vista? + Windows Live?. http://www.microsoft.com/windows/shop/specialoffers.mspx?ocid=TXT_TAGLM_CPC…