Why does this VGA cable have pin 9 while others are missing it?

There are two types of VGA cables: 14-pin and 15-pin. 14-pin cables will work in most applications, but 15-pin cables may be required for wider display compatibility. This product is a 15-pin VGA cable. Pin 9 was removed from 14-pin cables because the key signal became obsolete with modern computer monitors and was no longer used in the default applications of the VGA standard. However, Pin 9 has recently been reintroduced as a power supply pin to power circuity in certain displays. This pin does not power an entire display, but it is required for data communication between the display and the computer. The data communication between the display (Display Data Channel or DDC) communicates display information such as maximum resolution and the name of the display. If you are unsure which cable type you require for your application, you can check the manufacturer specifications. Typically, computer monitors only require 14-pin cables and televisions require 15-pin cables. If you require a 14-pin VGA cable, see the following FAQ: http://www.startech.com/faq/vga_cables_14_pin_vs_15_pin_14_pin_version .