why X works without xorg.conf , because i renamed it and X still works
another question, why there is no "initrd" file in /boot ,, i thought it is needed before mounting the actual root filesystem.
thanks in advance

Initrd is only needed if you need to load modules before the kernel gets loaded to help with booting.

Xorg.conf is mostly autodetected with the more recent versions of X, its only needed if you have specific settings you need to change.

thank you ,, that was quick and sufficient

Newer versions of X now do a lot of probing of your system at startup so that your hardware can be automatically configured. In many cases there is now no need for an xorg.conf at all. It is still possible to configure X using xorg.conf or files in xorg.conf.d which can be useful for some device dependent configuration (e.g dual monitor setups, custom mouse configuration). You can see what X determines about your system from autoprobing by running 'X -configure'.
You do not require an initrd if you are using the huge kernel as a lot of device support is compiled into it. You do require an initrd if you use the generic kernel.

i'm using a huge kernel this means it supporting a big range of devices, if i want to compile a kernel specific to my hardware (video, sound, lan, wireless,...) is there a command to show me all the models i need to choose in the new compiled kernel

Custom kernel compiles can be fun and instructive and perhaps necessary for some hardware, but these days I do not bother. The generic kernel with an initrd serves my needs. /usr/share/mkinitrd/mkinitrd_command_generator.sh is your friend, a most excellent tool from Alien_Bob. You could also use this tool to get information on what needs to be included in a custom kernel so that you can successfully boot.

i'm going to try this script, sounds nice as usual with Alien_Bob. Sometimes i feel that Alien_Bob doing things he wished somebody did for him when at his first days learning linux