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  Upping Vcore, CPU Overvolting Explained 
  Mar 06, 2002, 07:30am EST 

How Your CPU Thinks

By: Dan Mepham

Most of us are aware that CPUs, and indeed, all computer equipment, deal only in binary; 0s and 1s. Your CPU has no vocabulary for numbers as we know them, only 0s and 1s. Because of the way we’ve designed them, CPUs produce results that are understood by us (base 10), without really knowing they’re doing it. Our entire digital world is based entirely on this premise, this Boolean logic.

But what exactly constitutes a 0 or 1 inside a CPU? Many of you have likely heard the Off/On analogy, but what represents an Off or On? How does a gate in your CPU know when it’s off or on, 0 or 1?

The answer here is voltage. In a CPU, we have a low voltage, and a high voltage. These represent a logic low (0), and a logic high (1). If a gate wants to output a ‘1’, it outputs a logic high voltage. If it wants to output a ‘0’; a logic low voltage.

These voltages are generally referred to in more compact ways in datasheets, though. Logic low, which is usually 0V, is referred to as VSS. Logic high is referred to as VCC, or sometimes VDD or VCORE. The value of VCC will vary from device to device, and largely depends on the transistor technology used. When you talk about the core voltage of a Pentium 4 being 1.700V, this is the voltage to which you are referring. VCC for a Pentium 4 is 1.700V, while VCC for an old Pentium II may have been 2.800V.

So a typical gate, then, will look at the voltages of its inputs. If it sees a voltage of about VCC, it treats that as a logical 1. If it sees VSS (0V), it treats it as a logic 0. Your CPU is nothing more than a huge array of ever-changing voltages, used to indicate 0s and 1s.

1. Introduction
2. How Your CPU Thinks
3. It's All About Tolerance
4. Transient States
5. Putting it All Together
6. Summary

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