I have just now realised why exactly Mac PCI Video card would not work in PC. IMB PC and compatibles have BIOS ROM on the motherboard that contains a simple startup code to help the computer to initialise and boot into OS. After OS has booted it does not use BIOS anymore (well, MS-DOS does...) Traditionally BIOS recognises and supports only CGA and EGA video adaptors (they are about 20 years old ) Because of the vast variety of possible VGA, SVGA and other hardware PC standard uses mapping of an ISA or PCI board's ROM chip into memory address of CPU (somewhere between C000h and E000h). At the very early stage of booting CPU scans this address range and if it finds a card's "piggy-back" ROM (by looking for a specific signature), it passes the control over (e.g. simply CALL 0xD004h) to this card's ROM and expects that the card does its necessary init and returns control back (RETURN). Obviously Mac video card ROM contains anything else but x86 CPU instructions so the PC will simply choke up and system will never even be able to show its startup screen. Even though OS includes hardware-specific drivers in software the system will never reach that stage as it heavily relies on video system being operational from the very early stage of the boot process. Now if somebody would explain why PC cards would not work in Mac without reflashing? Is the above applies to Mac booting process as well?