The philosopher Bertrand Russell once gave a public lecture on astronomy. He described how the earth orbits around the sun, and how the sun orbits an array of stars we call the Milky Way.
A little old lady in the audience got up and said, “What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise.”
Russell smiled, “What is the tortoise standing on?”
“You’re very clever, young man, very clever,” said the old lady, “but it’s turtles all the way down!” 
Our modern technological world is similar: it’s platforms all the way down. A platform—as defined by Bill Gates—is something you can stand on and build greater value than the value captured by the platform itself.
Since the late 1800s, we have been building successive platforms that have brought us to this day:
The creation of electric power plants and a dense distribution network enabled the creation of entire industries such as lighting, electric motors, radio, television and more;
Semiconductors and computers were built on top of the electric infrastructure, and led to the creation of open-source Unix software and network protocols;
These in turn enabled the creation of the internet;
All of these previous platforms led to the development of another one: cloud computing, which consists of computer servers in centralized locations distributing compute to any customer anywhere;
Cloud computing enabled the creation of new computing platforms such as Salesforce and Atlassian;
Atlassian enables an entire economy (and has become a platform itself) with apps built on top of it.
If our description of platforms resembles infrastructure, this is not accidental. Wikipedia defines infrastructure as “the set of fundamental facilities and systems serving a country, city, or other area, including the services and facilities necessary for its economy to function.”
In the past we have called many of our software businesses “infrastructure assets of the digital age” for this reason. These are of course superior to physical infrastructure in many ways: higher margin, scalable to the entire planet, and capable of generating high returns on invested capital.
What are the next steps in this progression? We will certainly see more multibillion-dollar companies built on top of existing platforms, but what’s most exciting are the up-and-coming empires using software to attack industries that have so far been impervious to disruption. We have investments in some candidates and expect more to make it to the public markets in coming years.
 From Stephen Hawking’s A Brief History of Time
[Note: This post is adapted from our Q1 2020 letter to investors.]