While most video cards are of the PCIe format, video cards come in other formats as well, including PCI and AGP.
Like all hardware, a video card requires a device driver in order to communicate with the operating system and other computer software.
The same process you'd use to update any sort of hardware applies to updating a video card driver.
A video card is a piece of computer hardware that's rectangular in shape with numerous contacts on the bottom of the card and one or more ports on the side for connection to video displays and other devices.
The video card installs in an expansion slot on the motherboard.
If a previously troublesome video card becomes stable when underclocked then it means that you have a hardware problem rather than a software problem.