F5   or   SHIFT  
This feature of DOS 6.0+ lets you bypass all commands in CONFIG.SYS and
AUTOEXEC.BAT.  DOS 6.2: Ctrl+F5 bypasses loading of DoubleSpace support.

During the System Startup Sequence, the message...

Starting MS-DOS...

...appears and the system pauses for 2 seconds.  If you press and release
F5 at this point, OR press and hold SHIFT, DOS displays...

MS-DOS is bypassing your CONFIG.SYS and AUTOEXEC.BAT files.

...and goes directly to a DOS command prompt.  If the CONFIG.SYS file
contains a MultiConfig Menu, you can press F5 at the menu prompt.

  Skipping DBLSPACE.BIN  
The DoubleSpace support driver, DBLSPACE.BIN, is automatically loaded
before CONFIG.SYS is executed.  If you need to disable DoubleSpace
support, you would need to rename it on the host drive before booting.
However, if you are running DOS 6.2+, just press  Ctrl + F5   at boot
time.  Of course, DOS won't be able to find your             
normal CONFIG.SYS and AUTOEXEC.BAT files (assuming that your drive C is a
swapped DoubleSpace volume).  So you may wish to make special "emergency"
versions in the root of the host drive (often drive H or I).

SWITCHES= (/N disables Clean Boot; /F skips the 2-second delay)
- -

Clean Boot