> However, Dennard scaling also says that the power density of a transistor remains constant. As transistors became smaller, more of the die became occupied by

> However, Dennard scaling also says that the power density of a transistor remains constant. As transistors became smaller, more of the die became occupied by transistors, causing more heat dissipation per unit area. After exhausting cooling options (think back to the TDP of those CPUs back in the late-90s/early 2000s), Dennard scaling died in the mid-to-late 2000s because of thermal issues. Dennard scaling says that power usage per transistor per clock cycle is constant; not power density. As transistors became smaller, an x% reduction in transistor area meant an x% reduction in power per transistor per clock cycle, which allowed clock cycles to increase dramatically to consume the same fixed heat dissipation budget. The breakdown was not from there being too many transistors per square millimeter, but from the breakdown of the direct relationship of transistor size to power consumption per clock cycle due to current leakage. An x% reduction in transistor area no longer causes an x% reduction in power consumption per clock cycle, meaning operating clock frequency is now fixed at your ability to dissipate heat, not your ability to shrink transistors.