|What is this in reference to? Many of the original 8086/8088 motherboards had sockets for ROM chips for BASIC or whatever else someone might think of to put on a chip. If no boot device was available the bios would go to the ROM chip.|
There were some ISA cards with an expansion bios for older computer bios' that couildn't see more than 1024 cylinders on a hard drive. Having that card allowed the bios to correctly see larger drives. I remember pulling a lot of those out of some of the original IBM pentium 60's that had that limitation.
Most of the good ISA IDE cards especially from Promise had an onboard bios that often extended drive support to larger drives. SCSI cards usually had their own bios too.
More modern add-on PCI ATA and SATA cards are the same way.
Back in the late 90's when everyone was worried about the Y2K bug there were some ISA add-on cards which kept the computer clock accurate past 2000.
In all cases the computer boots with the motherboard's bios and then hands off to these other bios' to do their thing.