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+## SETMAC.SYSTEM
+
+`SETMAC.SYSTEM` is a simple utility for setting the MAC address on an Uthernet-II card
+in an Apple //e or GS.
+
+It is intended to be placed in the top level directory of a ProDOS boot disk (ie: in
+the "volume directory"). 
+
+### Configuration File
+
+`SETMAC.SYSTEM` looks for a configuration file called `SETMAC.CFG` in the directory
+from which it was started.  If this file is not found, then `SETMAC.SYSTEM` will
+fall back to default values of assuming an Uthernet-II in slot 5 and using the
+MAC `00:08:0d:10:20:30`.  You will almost certainly want to change this.
+
+`SETMAC.CFG` is an extremely simple text file, which you can create in `EDIT.SYSTEM`
+or any ProDOS text editor that can save plain text files.  It consists of a single
+digit representing the slot where the Uthernet-II is installed, followed by a
+space, then the six byte MAC address in hex, with colons separating the octets.  A
+sample `SETMAC.CFG` file for an Uthernet-II in slot 3 could look like this:
+
+```
+3 01:02:03:aa:bb:cc
+```
+
+The parser is very simple minded so please stick to the formatting of the file as
+specified here, or you may have surprises!
+
+If the config file does not exist or is unreadble, `SETMAC.SYSTEM` will display
+a message explaining that it could not open the file so it is using default
+parameters and will pause awaiting a keypress to acknowledge this status.
+
+### Chaining `.SYSTEM` Files at Startup
+
+When ProDOS starts, it will automatically run the first `.SYSTEM` file it finds in
+the volume directory. This is often a file such as `BASIC.SYSTEM` but it can be
+any valid `.SYSTEM` file.
+
+Before `SETMAC.SYSTEM` terminates, it searches the volume directory to find the entry
+matching itself, and then scans forward looking for a `.SYSTEM` file. If it finds
+one it loads it into memory and starts it executing.
+
+If for example, one had the following files in order in the ProDOS volume directory
+on the boot volume:
+```
+PRODOS
+SETMAC.SYSTEM
+BASIC.SYSTEM
+```
+Then ProDOS would start `SETMAC.SYSTEM` on boot and `SETMAC.SYSTEM` would, in turn,
+start `BASIC.SYSTEM`.  Longer chains are possible, with other compliant programs
+such as the No Slot Clock Driver (`NS.CLOCK.SYSTEM`).