# A septillion CPU cycles a year

A septillion is a huge number, equal to 1024. Can anything man-made have a number that large? In fact, yes. A quick back-of-the-envelope calculation will show that in the whole world, the number of CPU cycles executed in a year exceeds a septillion.

A modern desktop or laptop CPU runs at over 1 GHz, or 1 billion cycles per second. A (non-leap) year has 365 × 86400, approximately 30 million, seconds. With hundreds of millions of personal computers and servers sold, the world surely has over 30 million of such CPUs running actively at any given moment. Multiply these three numbers together, and we get 1 septillion.

That was just a calculation based on my estimates of numbers. I don’t actually know the average clock speed of CPUs, or the number of active CPUs in the world. I am fairly sure that both numbers are underestimated, and the world could easily be executing 10, even 100 septillion CPU cycles a year.

While the number 1 septillion is almost unimaginably huge in human terms, it can be rather small in other contexts. For example in chemistry, the Avogadro constant is about 6.0 × 1023, which is the number of atoms in 12 grams of pure carbon-12. For example in information theory or combinatorics, the set of all 80-bit strings has just over 1 septillion elements.

What do these septillion CPU cycles accomplish for us? A large portion of them are simply idle cycles where the CPU clock keeps running but no calculations are performed. This is because the CPU is waiting for data from RAM or disk or the network, or waiting for more work from an end user. The remaining non-idle, useful CPU cycles are spent to support our increasingly digital lifestyle. They paint words and pictures on the screen, they immerse us in the virtual environments of games, they compress data for efficient storage, they encrypt data for privacy, and much much more. The CPU cycles take over the functionality traditionally done by other means – for example paper documents and photos, mechanical puzzle games, sports based on physics, microfilm, letter envelopes.

In a sense, a CPU cycle is a fundamental unit of computational work, and its importance in our lives has been growing. Since the 19th century, the cost of doing a calculation has steadily fallen with mechanical calculators, electronic calculators, and computers. As the availability of CPU cycles increased, new applications – such as graphics – arose to make use of them. As we head into the future, we can expect to see more CPU cycles executed per year, less cost per cycle, more cycles available to each person, and more interesting applications to make use of them.