81. Booting up secondary drives
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is very simple to Boot up disc drive 0, by pressing <Shift> <Break>, but
you cannot usually do this with, say, drive 1. (Some independent DFSs do
allow this, but not Acorn ones.) However, there is a way, which works as long
as you have a disc in drive 0 as well. Just insert this routine at the start
of whatever program the !BOOT file CHAINs - eg a menu utility. All you do to
Boot up drive 1 is to Boot up drive 0 as normal, but hold onto the <Shift>
key just a little longer than usual, until you see drive 1 start up. Do
release the <Shift> key as soon as drive 1 starts up, or it may go into a
harmless loop until you do let go. Needless to say, if you have a
double-sided drive, then this works just as well for drive 2 instead of 1.

 95 IF INKEY(-1)=0 THEN 100:REM Test for <Shift>.
 96 *DR.1
 97 *EXEC !BOOT
 98 END:REM You need this!
100 REM Start of main program.