Q. How can I configure my system to disable X Windows KDE during Linux system coming up / booting up?

A. Usually almost all Linux distribution use following runlevels for text and GUI mode:

=> Runlevel – 2/3 : Text mode
=> Runlevel – 5 : GUI mode

These modes are defined in /etc/inittab file.

Open file /etc/inittab
# vi /etc/inittab

Find out entry that read as follows:
id:5:initdefault:

Set the default runlevel to 3 (text mode)
id:3:initdefault:

Save and close the file

Reboot the system
# reboot

Now you will boot into text mode only. If you want to see GUI (KDE desktop) type the following command:
$ startx