diff --git a/docs/v4.0.0/MACHINE.md b/docs/v4.0.0/MACHINE.md
index 9543e472..9e826d14 100644
--- a/docs/v4.0.0/MACHINE.md
+++ b/docs/v4.0.0/MACHINE.md
@@ -25,6 +25,20 @@ The ROM is the only binary. It runs the same on the C engine and on the FPGA: on
 same behaviour. Assemble FORTH from the trailer and the node is a FORTH machine. Assemble Lisp
 and it would be a Lisp machine. The engine and the ROM do not change.
 
+### 1.1 What it is for
+
+This is an operating system, not a toy (Captain Bob, 2026-10-15). Once everything is assembled
+and compiled, the system is a multi-user, multitasking operating system. That is all the boot
+in section 3 makes.
+
+Then the system's init, `init.4th`, brings it up:
+- it turns on security;
+- it starts the system a module at a time and a node at a time;
+- whoever is logged in gets a prompt: Zuse, `rajames`, `00` to `09`, or whoever it is.
+
+From the prompt a user can do anything, in FORTH. The operating system's utilities are written
+in FORTH.
+
 ## 2. The ROM
 
 **What it does.** It reads a named blob and acts on its type: