By now I'm sure you've heard of SOI and about the problems AMD has had adopting this new technology. AMD believes so much in SOI that they've even paid IBM $20 million to help them out. SOI technology allows for silicon to run at higher frequencies while using less voltage than conventional silicon like that found in Intel processors or AMD's own K7 line of CPU's.

To understand SOI, you must first understand what a transistor is and how it functions. A transistor is a simple switch and it can either be on or off (on allows electricity to flow, off doesn't). When we quote the number of transistors in any given processor (the Athlon64 has 105.9 million), we're basically describing the number of switches the processor has.

All modern transistors (even SOI enhanced ones) are based MOS (Metal Oxide Semiconductor) technology. MOS means that a piece of metal is placed on an oxide which is itself a piece of silicon. Pure silicon does not conduct electricity so impurities are added which then allow the silicon to be conductive.

When high voltage is passed through the metal gate, the silicon becomes conductive and will allow current to pass through it, when the voltage is low, the silicon becomes an insulator. This is where the term "Semiconductor" comes from.

SOI and AMD

SOI is significant because in theory it will allow transistors to act much faster when switching between on and off, and has actually been under development for the last 30 years. SOI literally means that manufacturers will place a piece of silicon on top of an insulator (glass, silicon oxide, etc) then the transistor would be placed on top of the SOI. SOI reduces capacitance, and that makes switches operate faster, and that allows the electricity get from point-to-point with less of lag.

So simple. Yet so hard to implement. We're not going to dwell on how SOI is implemented on a processor as that is beyond the scope of this review.