diff --git a/src/interrupts.s b/src/interrupts.s
index 1573e59..848b80b 100644
--- a/src/interrupts.s
+++ b/src/interrupts.s
@@ -652,6 +652,15 @@ cop_ioctl:
 ; structure of the kernel. This allows the shell to be unloaded when running anoter
 ; program, and to restore its state when that program exits.
 ;
+; Internally, the kernel loads the environment from a serialized data file on SD,
+; called `shell.env`. This file consists of string keys and values, one each per
+; line, delineated by the `:=` character sequence. String keys are case-sensitive.
+; The SDK will provide library functions for managing the environment.
+;
+; The kernel also uses the data in the shell environment to determine which program
+; is loaded into memory as the shell -- rather than re-read the shell binary from
+; SD every time, it caches the PGZ file in memory and unpacks it as needed.
+;
 ; Arguments: None
 ; Return Value:
 ;		A: Environment bank