The windows version probably brings its own copy of Python plus tons of third party libraries
The linux tar.xz is 24M, and 147M uncompressed.
The translations alone are 57M, they look like this:
Code:
#: /home/kovid/work/calibre/src/calibre/devices/bambook/driver.py:352
#: /home/kovid/work/calibre/src/calibre/devices/bambook/driver.py:354
#: /home/kovid/work/calibre/src/calibre/devices/hanvon/driver.py:115
#: /home/kovid/work/calibre/src/calibre/devices/hanvon/driver.py:126
#: /home/kovid/work/calibre/src/calibre/devices/kobo/driver.py:426
#: /home/kovid/work/calibre/src/calibre/devices/kobo/driver.py:458
#: /home/kovid/work/calibre/src/calibre/devices/usbms/driver.py:335
#: /home/kovid/work/calibre/src/calibre/devices/usbms/driver.py:356
msgid "Removing books from device..."
msgstr "Bücher vom Gerät entfernen ..."
So tons of comments for every little string times 70+ languages = huge.