Replace PS/2 Trackball with USB optical mouse

Linux and Unix-Like Slackware
1

Running Slackware 13.37 original without updates.
Need to replace my trackball with optical mouse temporarily.
There is no xf86config file anylonger but xorg.conf file is produced automatically.
I see 2 "xorg.conf" files which can be and were modified on installation:
1) /etc/X11/xorg.conf-vesa and 2) /root/xorg.conf.new.
The descriptions for the mouse are:
1)

Section "InputDevice"
    Identifier  "Mouse1"
    Driver      "mouse"
    Option      "Protocol"    "PS/2"
    Option      "Device"      "/dev/mouse"
EndSection

2)

Section "InputDevice"
    Identifier  "Mouse0"
    Driver      "mouse"
    Option      "Protocol" "auto"
    Option      "Device" "/dev/input/mice"
    Option      "ZAxisMapping" "4 5 6 7"
End Section

Found changes for USB optical mouse to be:

Section "InputDevice"
    Identifier  "Mouse9"
    Driver      "mouse"
    Option      "Device" "/dev/input/mice"
    Option      "Protocol"    "IMPS/2"
    Option      "ZAxisMapping" "4 5"
EndSection
InputDevice "Mouse9" "SendCoreEvents"

Would someone explain a) which file to is actually used and if it is the one to modify, b) why it should be Mouse9 not Mouse0, c) what is ZAxisMapping, d) why it changes from 4 5 6 7 to 4 5 and e) is that last line in #2 correctly place/necessary?

2

You should be able to simple replace one mouse with the other without changing your Xorg configuration file.

ZAxisMapping relates to the mouse wheel (scroll-wheel). Technically, ZAxisMapping takes the input from the scrollwheel and maps it to button events. A 5 button mouse with no scrollwheel would perform like a scrollwheel on pressing buttons 4 and 5. "4 5" is most common because that's how many buttons most mice have. On a common mouse with two buttons and a clickable scroll-wheel, the left button is 1, right button is 2, scroll-wheel click is 3, scroll-wheel up is 4, and scroll-wheel down is 5. For people with side buttons use "6 7" since they count as 7 button mice.

3

Was able to pull the PS/2 plug on trackball and after changing PS/2 to IMPS/2 and adding the line:
Option "ZAxisMapping" "4 5"my optical mouse is working fine save I think I'll slow it down a bit. So THANKS.