Well for starters it's a type of memory that you can't really write to! Only Manufactures have written some type of information to the ROM chips!
Not too long ago you could only update it by physicly replacing it and buy a new one! But on today's technology you could really update it from the manufacturer's updating site, like in a familiar way as if you are updating drivers for your sound card,video card and etc...
That's why it's no longer called ROM chips but an EEPROM (Electrically Erasable Programmable Read Only Memory) or just EPROM (Erasable Programmable Read Only Memory)!
One of the major firmwares used on ROM, EEPROM is called BIOS(Basic Input /Output System) that includes a Power On Self Test (POST) task and other tasks that help the loading of the currently installed Operating System (XP,VISTA,Win7 and etc...)!
POST makes conection possible between devices and the operating system.