*The maximum file size for Linux ext2/ext3 (and other UNIX file system) is actually dependent on the choice of blocksize and hardware architecture.

The default format for GNU tar is defined at compilation time. You may check it by running tar --help, and examining the last lines of its output. Following is output command:

$ tar --help

....
...
....
*This* tar defaults to:
--format=gnu -f- -b20 --rmt-command=/usr/sbin/rmt
--rsh-command=/usr/bin/rsh
...