Skip to Content

Why CPUs Aren’t Getting Any Faster

Making computers faster means relying on the central processing unit (CPU) less than ever before.
October 12, 2010

The Central Processing Unit (CPU)–the component that has defined the performance of your computer for many years–has hit a wall.

In fact, the next-generation of CPUs, including Intel’s forthcoming Sandy Bridge processor, have to contend with multiple walls–a memory bottleneck (the bandwidth of the channel between the CPU and a computer’s memory); the instruction level parallelism (ILP) wall (the availability of enough discrete parallel instructions for a multi-core chip) and the power wall (the chip’s overall temperature and power consumption).

Of the three, the power wall is now arguably the defining limit of the power of the modern CPU. As CPUs have become more capable, their energy consumption and heat production has grown rapidly. It’s a problem so tenacious that chip manufacturers have been forced to create “systems on a chip”–conurbations of smaller, specialized processors. These systems are so sprawling and diverse that they’ve caused long-time industry observers like Linley Gwennap of Microprocessor Report to question whether the original definition of a CPU even applies to today’s chips.

In releasing Sandy Bridge, Gwennap observes, Intel has little to tout in terms of improved CPU performance:

Sure, they found a few places to nip and tuck, picking up a few percent in performance here and there, but it is hard to improve a highly out-of-order four-issue CPU that already has the world’s best branch prediction.

Instead, Intel is touting the chips’ new integrated graphics capabilities and improved video handling, both of which are accomplished with parts of the chip dedicated to these tasks–not the CPU instelf, which would be forced to handle them in software and in the process burn up a much larger percentage of the chip’s power and heat budget.

And what of general-purpose computing tasks? Gennap explains that here, paradoxically, the key to conquering the power wall isn’t more power–it’s less. Fewer watts per instruction means more instructions per second in a chip that is already running as hot as it possibly can:

The changes Intel did make were more often about power than performance. The reason is that Intel’s processors (like most others) are against the power wall. In the old days, the goal was to squeeze more megahertz out of the pipeline.

Today’s CPUs have megahertz to burn but are throttled by the amount of heat that the system can pull out. Reduce the CPU power by 10% and you can push the clock speed up to compensate, turning power into performance gains. Most CPU design teams are now more focused on the power budget than on the timing budget.

This means that, at least with this generation of chips, Intel is innovating anywhere but in the CPU itself.

As task-specific processors become more and more common, one can’t help but notice parallels with the world’s most powerful computer–the human brain.

The brain is full of high specialized processing cores as well as general computational capabilities. If silicon continues to follow the trend laid down by evolution, we can expect future “CPUs” in which the “central” processing unit is less and less important, and task-specific processors proliferate until Systems on a Chip come to resemble the tangled, sprawling metropolis that appears to have conquered massive parallelization in a way that computer scientists can now only dream of.

Follow Mims on Twitter or contact him via email.

Keep Reading

Most Popular

DeepMind’s cofounder: Generative AI is just a phase. What’s next is interactive AI.

“This is a profound moment in the history of technology,” says Mustafa Suleyman.

What to know about this autumn’s covid vaccines

New variants will pose a challenge, but early signs suggest the shots will still boost antibody responses.

Human-plus-AI solutions mitigate security threats

With the right human oversight, emerging technologies like artificial intelligence can help keep business and customer data secure

Next slide, please: A brief history of the corporate presentation

From million-dollar slide shows to Steve Jobs’s introduction of the iPhone, a bit of show business never hurt plain old business.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.