Urs Hölzle

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Urs Hölzle
Alma materETH Zurich
Stanford University
Scientific career
InstitutionsUniversity of California, Santa Barbara
ThesisAdaptive optimization for Self: Reconciling High Performance with Exploratory Programming (1994)
Doctoral advisorDavid Ungar
John L. Hennessy

Urs Hölzle (German pronunciation: [ˈʊrs ˈhœltslɛ]) is a Swiss software engineer and technology executive. He is the senior vice president of technical infrastructure and Google Fellow at Google. As Google's eighth employee and its first VP of Engineering, he has shaped much of Google's development processes and infrastructure.[1]


Before joining Google, he was an Associate Professor of Computer Science at University of California, Santa Barbara. He received a master's degree in computer science from ETH Zurich in 1988 and was awarded a Fulbright scholarship that same year. In 1994, he earned a Ph.D. from Stanford University, where his research focused on programming languages and their efficient implementation. Via a startup founded by Hölzle, David Griswold, and Lars Bak (see Strongtalk), that work then evolved into a high-performance Java VM named HotSpot, acquired by Sun's JavaSoft unit in 1997 and from there became Sun's premier JVM implementation.[2]

He led the design of Google's efficient data centers which are said to use less than half the power of a conventional data center.[3] In 2014 he received The Economist's Innovation Award for his datacenter efficiency work.[4] With Luiz Barroso, he wrote The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines.[5] Now in its third edition, the book is the most downloaded textbook at Morgan Claypool[6] and is widely used in undergraduate and graduate Computer Science education.

In June 2007, he introduced the Climate Savers Computing Initiative together with Pat Gelsinger which aimed to halve the power consumption of desktop computers and servers. In 2012, after mobile computing and enhanced awareness of datacenter energy costs had contributed to significant improvements in energy efficiency, CSCI merged with the Green Grid consortium.[7]

Also in 2007, he and Luiz Barroso wrote "The Case for Energy Proportional Computing" which argued that servers should be designed to use power in proportion to their current load, because they spend much of their time being only partially loaded. This paper is often credited for spurring CPU manufacturers to make their designs much more energy efficient.[8] Today, energy proportional computing has become a standard goal for both server and mobile uses.

In 2007, Hölzle announced that Google would be carbon neutral starting that year, using individually selected and monitored carbon offset projects.[9] In the same year, Google started the RE<C initiative ("Renewable Energy less than (cheaper than) coal")[10] to develop cheaper forms of renewable energy, but four years later Hölzle announced the end of that strategy, dropping development of "solar thermal" electricity (for example with BrightSource Energy) because it was not keeping pace with the rapid price decline of another solar technology – photovoltaics.[11] Starting in 2010[12], Google began buying renewable energy from new wind and solar farms to cover the energy needs for all its datacenters.[13] Since 2017 it has been buying enough renewable energy to offset 100% of its usage[14] and now is the world's largest corporate buyer of renewable energy.[15]

Starting in 2005, Hölzle's team began to develop datacenter networking hardware because off-the-shelf network equipment could not scale to the demands of large datacenters. Using Clos network topologies based on commodity switch chips, these datacenter networks scaled from an initial 10 Tbit/s to 1,000 Tbit/s a decade later.[16] Initially esoteric and kept a secret, today this approach is standard for large datacenter networks; virtually all hyperscale datacenter operators use similar approaches [17].

In 2012, Hölzle introduced "the G-Scale Network" on which Google had begun managing its petabyte-scale internal data flow via OpenFlow, an open source software system jointly devised by scientists at Stanford and the UC Berkeley and promoted by the Open Networking Foundation. The internal data flow, or network, is distinct from the one that connects users to Google services (Search, Gmail, YouTube, etc.). In the process of describing the new network, Hölzle also confirmed more about Google's making of its own networking equipment like routers and switches for G-Scale; and said the company wanted, by being open about the changes, to "encourage the industry — hardware, software and ISP's — to look down this path and say, 'I can benefit from this.'" He said network utilization was nearing 100% of capacity, a dramatic efficiency improvement.[18]

He is credited for creating Google Gulp for April Fool's Day in 2005.

He is member of the National Academy of Engineering,[19] and a Fellow of the Association for Computing Machinery (2009)[20], the AAAS (2017)[21], and the Swiss Academies of Arts and Sciences.[22] He is a board member of the US World Wildlife Fund.[23]


  1. ^ "I'm Feeling Lucky", Doug Edwards, Houghton Mifflin 2012
  2. ^ Google: Management Team
  3. ^ Google's Green Datacenter
  4. ^ Economist, December 6, 2014
  5. ^ Luiz André Barroso and Urs Hölzle, The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, Morgan & Claypool, 2009. ISBN 9781598295573
  6. ^ "Most popular downloads" https://www.morganclaypool.com/action/showMostReadArticles?journalCode=cac&
  7. ^ "The Green Grid and Climate Savers Will Merge" https://www.datacenterknowledge.com/archives/2012/07/20/the-green-grid-climate-savers-computing-initiative-merge
  8. ^ "Server Efficiency: Aligning Energy Use With Workloads", Datacenter Knowledge, June 12, 2012
  9. ^ "Carbon neutrality by end of 2007" https://googleblog.blogspot.com/2007/06/carbon-neutrality-by-end-of-2007.html
  10. ^ "RE<C Initiative" https://www.google.org/rec.html?theme=greenz_dev
  11. ^ "Google cans concentrated solar power project", REVE, November 24, 2011. Retrieved 2012-05-29.
  12. ^ "Google inks 20-year deal to buy wind power for data centers" https://www.infoworld.com/article/2625618/google-inks-20-year-deal-to-buy-wind-power-for-data-centers.amp.html
  13. ^ Google's Green PPAs https://static.googleusercontent.com/media/www.google.com/en//green/pdfs/renewable-energy.pdf
  14. ^ "100% renewable is just the beginning" https://sustainability.google/projects/announcement-100/
  15. ^ "Tech giants power record surge in renewable energy sales" https://www.theguardian.com/environment/2020/jan/28/google-tech-giants-spark-record-rise-in-sales-of-renewable-energy
  16. ^ "Jupiter Rising: A Decade of Clos Topologies and Centralized Control in Google’s Datacenter Network" https://research.google/pubs/pub43837/
  17. ^ https://engineering.fb.com/production-engineering/introducing-data-center-fabric-the-next-generation-facebook-data-center-network/
  18. ^ Levy, Steven, "Going With the Flow: Google's Secret Switch to the Next Wave of Networking", Wired, April 17, 2012. Retrieved 2012-04-17.
  19. ^ > NAE press release
  20. ^ ACM Fellows>Urs Hoelzle, Association for Computing Machinery webpage.
  21. ^ AAAS 2017 Fellows, AAAS webpage.
  22. ^ Full members>Hölzle, Dr Urs, SATW webpage.
  23. ^ Urs Hölzle. WWF webpage.

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