Processor Voltage

Processor voltage today is not a huge concern to the normal user. The only people who really concern themselves with it are those who overclock their system and sometimes fine-tune the voltages going to their processors in order to garner some extra speed and improve stability. So, this article is more of a reference.

Why does the voltage of your CPU even matter?

  • The more power the CPU takes, the more heat it creates. Heat is not good on the processor and can be a barrier in creating fast processors. So, lowering the voltage in fast chips reduces the heat. This is why newer processors are operating at much lower voltages than processors in the past.

  • Since laptops run on batteries, the amount of power consumed by the processor is a large factor. The lower the voltage, then, the longer the battery will last. Often manufacturers will fine-tune the voltage requirements of their processors in order to release mobile versions for use in notebooks.

  • Many times, large companies are running hundreds of PC’s at one time, therefore the amount of power used is a concern.

Dual Voltage

Older processors typically ran at one voltage, 5 volts. There was nothing else. As chips got faster and power became a concern, designers dropped the chip voltage down to 3.3 volts. Then, as chips got even faster and more powerful, there was a need to go below 3.3 volts. So, designers began to incorporate a split rail design, or dual voltage. In these chips, the external I/O voltage is 3.3 volts so that it is compatible with other motherboards and their components. The core voltage, then, is lower, maybe 2.9 or 2.5 volts. So, the chip operates at 2.5 volts while it interfaces with the motherboard at 3.3 volts. This keeps motherboard designs the same. The only components that changes is the voltage regulator that supplies the correct voltage to the CPU socket.

The core voltage is always changing with new processor designs. The voltage regulator converts the power to the correct core voltage for the processor in the socket or slot. Besides the actual processor interface, this voltage regulator is a major reason for the list of processors a motherboard supports. The voltage regulator is designed to supply only certain voltages, so a processor that demands something not deliverable by the voltage regulator will not be supported.

Voltages of Specific Processors

Here is a table with the voltages of most common CPU’s:

Specific Voltages
ProcessorExternal VoltageCore Voltage
80386SX (DX)55
80486DX (SX)55
Intel 486DX255
AMD, Cyrix 486DX23.33.3
486DX4 (All makes)3.33.3
5×86 (AMD, Cyrix)3.453.45
Pentium 60, 6655
Pentium 75-2003.3/3.523.3/3.52
Pentium MMX3.32.8
AMD K53.523.52
Pentium Pro-1503.13.1
Pentium Pro-166+3.33.3
Pentium II (Klamath)3.32.8
Pentium II Deschutes/ Celeron Mendocino3.32.0
Pentium iii (Katmai)3.32.0
Pentium iii (Coppermine)3.31.65-1.75*
Celeron II (Coppermine 128)3.31.5-1.65*
Pentium IV – 423 pin package3.31.75*
Pentium IV – 478-pin, 256KB L23.31.75*
Pentium IV – 478 pin, 512 KB L23.31.5-1.525*
AMD Athlon (Socket A)3.31.6-1.8*
AMD Athlon XP (Socket A)3.31.75*
AMD Athlon (Slot A)3.31.6-1.8*
AMD Duron (Socket A)3.31.6
AMD K6-2+ / K6-III+3.31.8-2.0*
AMD K6-III3.32.2
AMD K6-2 w/ 3DNow!3.32.2
AMD K6 266/ 3003.32.2
AMD K6-(166,200)3.32.9
AMD K6-2333.33.2

An Asterisk (*) denotes that the voltage of the processor depends on the internal revision and the clock speed of the chip.  Please check the chip itself in order to find the correct voltage to run it at.

Factory Overclocking

Recently, Intel and AMD have found that by raising the operating voltage of their chips, they can push the clock speed higher, and thus gain more of a profit from the chip.  Overclockers have been doing the same things for years now.  In the recent Intel and AMD line of processors, the operating voltage raises with clock speed, so be sure to check the voltage of your new chips before installing them.  The rule of thumb is: The faster the chip, the higher the voltage it will need. This is offset, though, by internal re-designs such as making the transistor density lower. Bringing the transistors closer together and improving processor design can allow you to increase the speed of the processor without increasing the voltage. So, of course, once technology advances, a chip with new technology might need only 1.4V to operate, while one with old technology might need 1.75V or even 1.8V.

User Overclocking

Like I said before, it is typically only the overclockers that need to concern themselves much with processor voltage. As state above, increasing the voltage delivered to the processor core can aid in increasing the speed of the processor. If one overclocks their processor and experiences instability, increasing the core voltage can improve the situation and allow it to run with stability. But, with increased voltage comes increased heat, so there is always a tradeoff here and adequate cooling is an absolute necessity.

One can increase the core voltage through their motherboard’s CMOS. Most boards have a range which they will allow you to increase the vore voltage, and in certain increments. you can always check the specs of a motherboard in advance of buying it to see how much room you have in the core voltage and in what increments it will allow you to increase it. Smaller increments allow you more flexibility to do this and not overheat your chip. Many motherboards will also allow you to increase the I/O voltage as well. This is helpful in some overclocking situations in order stabalize your I/O devices.

For more information on overclocking, check out our article on the subject.

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