Atari 400 Technical Reference Manual page 105

G. Same as power-up step 18, except instead of booting the
diskette software, a JSR is executed through the vector DOSINI
[OOOCl if the diskette-boot was successfully completed during the
Power-up initialization. See Section 10 for details of the
diskette-boot process.
H. Same as power-up steps 19 and 20.
Note that the initialization procedures and main entries for all
software entities are executed at every system reset as well as
at p
0
we
r up (s e est e p s 14, 1 7, 18, 20
I
F an d G)' 1ft h
e
user-supplied initialization/startup code must behave differently
in response to system reset than it does to power-up, then the
warmstart flag WARMSr
[0008J
should be interrogated; WARMST
=
0
means power-up entry, else system reset entry.
OPERATING SYSTEM C016555 -- Section 7
120