[CentOS] halt versus shutdown

> I'm quite sure that in original Berkeley Unix, as on the VAX 11/780, halt
> was an immediate halt of the CPU without any process cleanup or file system
> umounting or anything.   Early SunOS (pre-Solaris) was like this, too.
> 
The SunOS 4.1.2 man page for halt says 

   NAME
      halt - stop the processor
   SYNOPSIS
    /usr/etc/halt [ -oqy ]
   DESCRIPTION
        halt writes out any information pending to the disks and then
        stops the processor.
         halt normally logs the system shutdown to the system log 
          daemon, syslogd(8), and places a shutdown record in the 
          login accounting file Ivar/admlwtmp. 
          These actions are inhibited if the -0 or -q options are present. 

The BSD 4.3 (that ran on VAXen) man pages say largely similar things:

https://www.freebsd.org/cgi/man.cgi?query=halt&apropos=0&sektion=0&manpath=4.3BSD+Reno&arch=default&format=html

Everything is somewhere on the net :-)

P.