It’s been nearly eight years since Intel canceled Tejas and announced its plans for a new multi-core architecture. The press wasted little time in declaring conventional CPU scaling dead — and while the media has a tendency to bury products, trends, and occasionally people well before their expiration date, this is one declaration that’s stood the test of time.

To understand the magnitude of what happened in 2004 it may help to consult the following chart. It shows transistor counts, clock speeds, power consumption, and instruction-level parallelism (ILP). The doubling of transistor counts every two years is known as Moore’s law, but over time, assumptions about performance and power consumption were also made and shown to advance along similar lines. Moore got all the credit, but he wasn’t the only visionary at work. For decades, microprocessors followed what’s known as Dennard scaling. Dennard predicted that oxide thickness, transistor length, and transistor width could all be scaled by a constant factor. Dennard scaling is what gave Moore’s law its teeth; it’s the reason the general-purpose microprocessor was able to overtake and dominate other types of computers.

CPU scaling showing transistor density, power consumption, and efficiency. Chart originally from The Free Lunch Is Over: A Fundamental Turn Toward Concurrency in Software

The original 8086 drew ~1.84W and the P3 1GHz drew 33W, meaning that CPU power consumption increased by 17.9x while CPU frequency improved by 125x. Note that this doesn’t include the other advances that occurred over the same time period, such as the adoption of L1/L2 caches, the invention of out-of-order execution, or the use of superscaling and pipelining to improve processor efficiency. It’s for this reason that the 1990s are sometimes referred to as the golden age of scaling. This expanded version of Moore’s law held true into the mid-2000s, at which point the power consumption and clock speed improvements collapsed. The problem at 90nm was that transistor gates became too thin to prevent current from leaking out into the substrate.

Intel and other semiconductor manufacturers have fought back with innovations like strained silicon, hi-k metal gate, FinFET, and FD-SOI — but none of these has re-enabled anything like the scaling we once enjoyed. From 2007 to 2011, maximum CPU clock speed (with Turbo Mode enabled) rose from 2.93GHz to 3.9GHz, an increase of 33%. From 1994 to 1998, CPU clock speeds rose by 300%.

Next page: The multi-core swerve