option ROM is a network boot ROM. The option ROM contains the program required to download the boot code. The original IBM Personal Computer ROMs hooked INT 18H (originally to invoke Cassette BASIC) and INT 19H, as these two interrupts were used for the boot process. INT 19h is called to initiate the boot process, and INT 18h was called to start Cassette BASIC from ROM when the boot process found that none of the possible boot devices was bootable. Originally, by hooking INT 18h, the network adapter ROM would try to boot from the network when all other boot devices (floppy drives, hard drives, etc.) had failed. By hooking INT 19H, the network adapter ROM would attempt to boot from the network before any other devices. The BBS specifies that the NIC option ROM does not hook INT 19h, but instead the BIOS 19h handler should call the BEV, which will then download the boot code. Video The Video BIOS provides some basic display services for BIOS and operating systems, for example INT 10H (Legacy BIOS), VBE (Legacy BIOS) and UEFI GOP. The original IBM PC BIOS included integrated support for the IBM CGA and MDA video adapters (and did not support option ROMs at all), so those video cards had no option ROMs. The CGA and MDA support in the BIOS proper was maintained through the IBM PC XT and PC AT product lines (which did support option ROMs), so that those cards worked (with full BIOS support) in those machines. The first PC video adapter card that had an option ROM was the IBM EGA, introduced in 1984 with the IBM PC AT. (The Hercules Graphics Card had no option ROM and no BIOS support except for its MDA-compatible features, for which it relied in the IBM-supplied MDA support in the main BIOS.) Most subsequent PC video adapters were supported by option ROMs, although VGA and MCGA integrated onto PS/2 motherboards may have used integrated BIOS support. Once integrated Super VGAs (SVGAs), integrated on clone PC motherboards, were being provided by separate companies than the systems themselves, it became common for the SVGA vendor-provided video BIOS to be included as a separate option ROM module on the same BIOS chip as the main system BIOS (provided by a third separate company). UEFI Option ROMs The PCI spec allows multiple option ROM images on the same device. These