MS/DOS 6.0: Interactive Startup.

     When MS/DOS 6.0 startup up it tells you "Now Starting MS/DOS ..."

     At this point you have several choices.  Do nothing and it will
     simply load as usual. But if you press {F5} or hold the Shift key
     down, MS/DOS 6.0 will ignore both your CONFIG.SYS and
     AUTOEXEC.BAT files and come up 'plain vanilla.' Or you may press
     the [F8] key. This will let you single step through your
     CONFIG.SYS file executing or not each line. 
     Great for debugging. No more lockups after typos, requiring you
     to scrounge for you bootable DOS diskette. For the security
     conscious, there are options you can place on a SWITCHES= command
     in your CONFIG.SYS file to disable these startup hot keys and the
     two second time delay before it starts to read CONFIG.SYS at all.

     SWITCHES=  /W  /K  /N  /F
     /N causes the hot keys to be ignored
     /F bypasses the two second pause, resulting in immediate startup

     The other two switches don't relate to immedicacy.

     /W is a Windows compatibility switch.  It compensaties for your
     cleverness, if any, in placing WINA20.COM where Win 3.1 can't
     find it.
     
     /K is an ANSI.SYS compatibility switch.
     
     /F bypasses the two second pause, resulting in immediate startup