TheCPU core voltage (VCORE) is thepower supplyvoltage supplied to the processingcores ofCPU (which is adigital circuit),GPU, or any other device with a processing core. The amount ofpower a CPU uses, and thus the amount of heat it dissipates, is the product of this voltage and thecurrent it draws.In modern CPUs, which areCMOS circuits, the current is almost proportional to theclock speed, the CPU drawing almost no current between clock cycles. (See, however,subthreshold leakage.)
To conserve power and manage heat, manylaptop anddesktop processors have apower management feature that software (usually theoperating system) can use toadjust the clock speed andcore voltage dynamically.
Often avoltage regulator module converts from 5V or 12 V or some other voltage to whatever CPU core voltage is required by the CPU.
The trend is towards lower core voltages, which conserve power. This presents the CMOS designer with a challenge, because in CMOS the voltages go only to ground and the supply voltage, the source, gate, and drain terminals of theFETs have only the supply voltage or zero voltage across them.
TheMOSFET formula: says that the current supplied by the FET is proportional to the gate-source voltage reduced by athreshold voltage, which depends on the geometrical shape of the FET's channel and gate and their physical properties, especiallycapacitance. To reduce (necessary to reduce supply voltage and increase current) one must increase capacitance. However, the load being driven is another FET gate, so the current it requires is proportional to capacitance, which thus requires the designer to keep capacitance low.
The trend towards lower supply voltage therefore works against the goal of high clock speed.Only improvements inphotolithography and reduction in threshold voltage allow both to improve at once. On another note, the formula shown above is for long channel MOSFETs. With the area of the MOSFETs halving every 18-24 months (Moore's law) the distance between the two terminals of the MOSFET switch called the channel length is becoming smaller and smaller. This changes the nature of the relationship between terminal voltages and current.
Overclocking a processor increases its clock speed at the cost of system stability. Withstanding higher clock speeds often requires higher core voltage at the cost of power consumption and heat dissipation. This is called"overvolting".[1] Overvolting generally involves running a processor out of its specifications, which may damage it or shorten CPU life.
Adual-voltageCPU uses asplit-rail design so theprocessor core can use a lower voltage, while the externalInput/Output (I/O) voltages remain at 3.3 volts (or 5 volts for older CPU's) for backwards compatibility.
Asingle-voltage CPU uses a single power voltage throughout the chip, supplying both I/O power and internal power. All[citation needed] CPUs before thePentium MMX are single-voltage CPUs.
Dual-voltage CPUs were introduced for performance gain when increasingclock speeds and finersemiconductor fabrication processes caused excess heat generation and power supply concerns, especially regardinglaptop computers. Using avoltage regulator, the external I/O voltage levels were 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 olderIntelP5Pentium processors that are typically intended for use in a mobile environment. It refers to splitting thecore 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. AllPentium MMX and later processors adopted this so-called split rail power supply.
Besides CPU core voltage, modern CPUs often have many different voltages for components. One of the reasons behind this was that modern CPUs integrate numerous components that were once separate integrated circuits (ICs). As semiconductor technology has advanced, functions such as CPU cores, memory controllers, PCIe controllers, and, in some cases, integrated graphics, have been consolidated into a single CPU package. However, despite the overall reduction in transistor size, not all voltage requirements scale down proportionally. Some components within the CPU may still require higher voltages to operate efficiently, necessitating the use of multiple voltage levels to power various components effectively.
Some examples of different voltages in a modern CPU: