One interesting aspect of the implementation of sam is that there are actually two different text representations. What's discussed here is the part in the main sam process, but there's another data structure in the samterm process that contains only those sections of the file that have actually been displayed in the samterm GUI.
This meant that you could run sam and samterm on opposite ends of a slow link and still be able to edit very large files. The remote sam process loads the file into the data structure described in the original article. samterm only loaded (over the slow link) the section of the file needed to draw a window containing the part of the text the user was looking at. As you moved around the file samterm would fill in parts of the data structure with the text you needed to see.
This meant that you could run sam and samterm on opposite ends of a slow link and still be able to edit very large files. The remote sam process loads the file into the data structure described in the original article. samterm only loaded (over the slow link) the section of the file needed to draw a window containing the part of the text the user was looking at. As you moved around the file samterm would fill in parts of the data structure with the text you needed to see.
The data structure used on the samterm end is called a Rasp: a file with holes. See https://plan9port.googlesource.com/plan9/+/refs/heads/master...