This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
An alias to MachTen can be installed in the Startup Items folder in your
System Folder. This will start MachTen every time your Mac boots. You can
even run Power MachTen without the Finder.
MachTen can also be configured to boot instead of the Finder. This is most
beneficial if a Macintosh is to be used fundamentally as a UNIX system and
few, if any, desktop operations are needed. Running MachTen as the Finder
saves precious RAM and processing resources. To maintain the Desktop, Finder
must assume control of the system every few seconds in order to update
folder file information, handle changes in the volume structure, and perform
general bookkeeping for the Desktop. It is possible to run MachTen without
Finder and, if needed, start the Finder from MachTen.
While this idea is interesting and has a certain academic quality to it (in
that you are able to get the most possible from your Macintosh for your UNIX
processing), it may only have appeal for more vigorous UNIX enthusiasts.
This whole mechanism becomes much more interesting, however, if a Macintosh
is to be used in an environment where access to the Macintosh desktop and
its MachTen files need to be controlled. Running MachTen as the Finder
forces every user to log in in the traditional UNIX manner. To configure
your Macintosh to start MachTen instead of Finder upon power ON, please see
the Tenon Technical Note, "MachTen as Finder".