A dual-voltage CPU uses a split-rail design so the processor core can use a lower voltage, while the external Input/Output (I/O) voltages remain at 3.3 volts for backwards compatibility.
A single-voltage CPU uses a single power voltage throughout the chip, supplying both I/O power and internal power. As of 2002 Microprocessor#Market statistics, most CPUs are single-voltage CPUs. All[citation needed]CPUs before the Pentium MMX are single-voltage CPUs.
Dual-voltage CPUs were introduced for performance gain when increasing clock speeds and finer semiconductor fabrication processes caused excess heat generation and power supply concerns, especially regarding laptop computers. Using a voltage regulator, the external I/O voltage levels was transformed to lower voltages to reduce power draw, resulting in less heat for the ability to operate at higher frequencies.
VRT is a feature on older Intel P5 Pentium processors that are typically intended for use in a mobile environment. It refers to splitting the core voltage supply from the I/O voltage. A VRT processor has a 3.3 V I/O and 2.9 V core voltage, to save power compared to a typical Pentium processor with both I/O and core voltage at 3.3V. All Pentium MMX and later processors adopted this so-called split rail power supply.
VisualSim can model these specific CPU voltages with the Power_Manager as the baseline block as separate devices. This will allow power for the CPU to be controlled independently of the I/O voltages, which need to be at the specification level.
Web: https://en.wikipedia.org/wiki/CPU_core_voltage