Atari ST series Technical Reference Manual page 272

Get GEMDOS Version Number
Sversion()
This function returns the GEMDOS version number. This number refers
only to the version of GEMDOS, not to the GEM or TOS version in gen­
eral.
C macro format
int version;
version = Sversion();
Machine language format
move.w # $ 3 0 ,-(sp )
trap #1
addq.l #2,sp
Inputs
None
Results
D O version word
264
Sversion
A 16-bit code that indicates the GEMDOS version
number. The major version number is stored in the
low byte, and the minor revision number in the
high byte.
Opcode = 48 ($30)