default boot vs. safe mode

[Jan.Stary at ff.cuni.cz]

Hello,

I wonder what exactly is the difference between booting the 'default mode'
and 'safe mode' from the initial booting menu in -CURRENT.

Because, with 'default' it _always_ hangs for me, but with 'safe' I
_never_ had a problem. Is it just setting some kernel variables 
(like /etc/sysctl.conf)?

It's an Acer Aspire 1304XC laptop, Athlon XP.

Thank you.

	Jan