Thank you very much for this hint!
I now exchanged the *.osm files by *.osm.bz2 and removed the unzip command:


d:
cd \map
rem wget http://download.geofabrik.de/osm/europe.osm.bz2

java -Xmx1600m -cp .\Osmosis\osmosis.jar;.\Osmosis\lib\default\commons-logging-1.1.1.jar;.\Osmosis\lib\default\commons-compress-1.0.jar;.\Osmosis\lib\default\jpf-1.5.jar org.openstreetmap.osmosis.core.Osmosis --read-xml file="europe.osm.bz2" --bounding-box idTrackerType=BitSet top=60 left=4 bottom=47 right=16 --write-xml file="Centraleurope.osm.bz2"

java -Xmx1600m -jar splitter.jar --max-nodes=600000 Centraleurope.osm.bz2

java -Xmx1600m -jar mkgmap.jar --max-jobs --reduce-point-density=10 --description=OSM_DE --country-name=centraleurope --country-abbr=EU --name-tag-list="name:de,name,int_name" --style-file=.\My_Style\ --generate-sea=multipolygon --family-id=1331 --product-id=1 --series-name=OSM_Germany --family-name=OSM_Germany --area-name=Germany --overview-mapname=OSM_Centraleurope --net --gmapsupp --tdbfile --route --add-pois-to-areas --road-name-pois=0x640a --draw-priority=25 --latin1 --make-opposite-cycleways --remove-short-arcs -c template.args My.typ
pause

This needed only a few GBytes of drive space. A drawback is, that it took much more time (about 17 hours on my computer compared to an approximate “overnight job” before). Can I somehow use the second core of the CPU also for Osmosis? The resulting gmapsupp.img seemed to be ok, as a first test with my garmin indicated.

What I don’t understand is: Both gmapsupp.img-files have the same length, but are not equal on a binary level.