Achieving stability at extended operating speeds often requires increasing voltage levels, and sustaining faster processor speeds can demand a greater core voltage. Similarly, faster chipset operating speeds can often be sustained through a bump in input/output voltage. Several of the latest DDR memory-based motherboards also allow manipulation of memory bus voltage levels. This feature was originally implemented to preserve compatibility with early DDR modules, but the ability to change memory voltage levels has led to significant improvements in stability. Overclocking enthusiasts have exploited the potential for maximizing operating frequencies in this way.
Any increases in voltage levels are potentially hazardous. Most current .18- and .25-micron processor core architectures can operate within a 10 percent variance from the default specification, but added stresses require extra measures to protect long-term system stability. Cooling plays an integral role in the voltage manipulation process.
Any increases in voltage levels produce additional heat in the core circuitry. While all circuits can cross certain thermal thresholds, additional cooling is often required to prevent damage from temperature variations. Processor coolers, heat transfer compounds, case fans, and case design can all affect the cooling capabilities of a system. Further discussion of choices in these areas can be found in Chapter 8 dedicated to cooling technologies.
A phenomenon called electron migration can lead to system failure as a result of voltage increases. Electron migration results when moving electrons are displaced across integrated circuit trace routes. As fabrication technologies improve, die size becomes critical in determining maximum voltage tolerances. Smaller die sizes produce narrower trace routes, thus reducing the processor's ability to cope with the stresses of electron migration. As the circuits get smaller, voltage-level tolerances are lowered exponentially. Chapters 6, 7, and 8, detail system-specific information, including information about maximum voltage levels.