This is the beginnings of a alternative version of the PDP-7 Unix

system which corresponds to a later development point, around mid-1971,
where the system had lost the "dd" directory and gained . and ..
entries. This is close to the system as described in
http://www.tuhs.org/Archive/PDP-11/Distributions/research/McIlroy_v0/UnixEditionZero.txt
except there are no pathnames.

To use this version: cd build; make alt; make altrun

src/cmd/init.s

@@ -124,8 +124,12 @@ login:
 2:
    lac nchar
    sys setuid		" Set the user's user-id
-   sys chdir; dd	" and change into the "dd" directory
-   sys chdir; dir
+#ifdef NO_DD
+   sys chdir; dotdot	" Change into the root directory (out of system)
+#else
+   sys chdir; dd	" Change into the "dd" directory
+#endif
+   sys chdir; dir	" and then the user's home directory
 
    lac d2		" Close file descriptor 2
    sys close
@@ -249,6 +253,8 @@ m3:
 m3s = .-m3
 dd:
    <dd>;040040;040040;040040
+dotdot:
+   <..>;040040;040040;040040
 dir:
    040040;040040;040040;040040