The system BIOS contains many routines—called services—to initialize and
support the many devices that make up amodern PC. Services control things as
mundane as whether the NUM LOCK key is engaged at startup, to things as exotic-
sounding as the SDRAM precharge control, and beyond.
Unlike most types of PC software, BIOS routines rarely change. BIOS makers
update BIOS routines only to fix known bugs (thus enhancing stability) and to
add important functions such as compatibility with new hardware or hardware
standards.