I did a little digging and came up with the following.  Posix's 'whence'
disagrees with MPE/iX Shell & Utilities Reference Manual Vol 2 on a few. I
went with 'whence'.

The following commands are built into the shell. Building such commands
into the shell increases the performance of shell scripts and allows access
to the shell’s internal data structure and variables. For details on a
command, see its man page. These internal commands have semantics
indistinguishable from external commands.
: . [ alias basename break callci cat cd chmod chown command continue cp
echo eval exec exit export false fc frombyte getopts jobs kill let ln ls mv
print printf pwd read readonly return rm set shift test time times tobyte
trap true type typeset umask unalias unset wait whence

POSIX.2 recognizes a subset of these commands as special built-ins. Syntax
errors in special built-in commands cause a non-interactive shell to exit
with the exit status set by the command. The special built-in utilities are:
: . break continue eval exec exit export readonly return set shift trap
typeset unset

As well as built-in commands, the shell has a set of predefined aliases:
functions hash history integer r suspend


On Thu, 19 Apr 2001 13:23:14 -0700, Gavin Scott <[log in to unmask]> wrote:

>The functionality of CALLCI.HPBIN.SYS along with many other commonly
>executed shell commands (including 'ls') was merged into the SH executable
>quite a while ago for performance reasons (specifically to eliminate the
>process creation overhead).

* To join/leave the list, search archives, change list settings, *
* etc., please visit http://raven.utc.edu/archives/hp3000-l.html *