As noted in the previous post in this series, memory in SQL Server is generally divided between query plans in the plan cache, and data in the buffer pool (other uses for memory in SQL Server are listed later in this post).
The official documentation tells us:
[T]he default setting for max server memory is 2,147,483,647 megabytes (MB).
Look carefully at that number. It’s 2 billion megabytes. In other words, we might think of it as either 2 million gigabytes, 2,048 terabytes, or 2 petabytes.
Randolph is writing this like we don’t all have multiple petabytes of RAM on each machine.