the specification discloses a system and related method for accessing basic input / output system routines in a computer system having a single microprocessor and multiple software streams , or a multiple microprocessor system . in particular , bios routines that modify shared variables , or groups of bios routines , are opened for use by a calling software stream to the exclusion of other software streams . after performing desired tasks , the calling software stream closes the bios routine or groups of routines , thus making them available to other software streams . in this way , access to shared variables using the bios routines is synchronized ensuring that overlapping access , and the corresponding potential for errors , is eliminated .