HP Kayak XU 04xx HP Kayak XU PC Workstation Technical Reference Manual Hardwar - Page 32

2 System Board Devices on the SM Bus Devices on the SM Bus Device PIIX4 SM Bus Master Serial EEPROM LM75 LM78 SDRAM slot 1 SDRAM slot 2 SDRAM slot 3 SDRAM slot 4 PLL SM Bus Address 10 A8, AA, AC, AE 90 5A A0 A2 A4 A6 D2 The System Management (SM) bus is used to monitor several of the hardware functions (such as voltage levels, temperature, fan speed, DIMM presence and type) of the motherboard. It is controlled by the SM bus controller located in the PIIX4 chip. Serial EEPROM This is the non-volatile memory which holds the default values for the CMOS memory (in the event of battery failure). The computer uses 4 Kbit of Serial EEPROM implemented within a single 512 ! 8-bit ROM chip. Serial EEPROM is ROM in which one byte at a time can be returned to its unprogrammed state by the application of appropriate electrical signals. In effect, it can be made to behave like very slow, nonvolatile RAM. It is used for storing the tatoo string, the serial number, and the parameter settings for the Setup program. When installing a new system board, the Serial EEPROM will have a blank serial number field. This will be detected automatically by the BIOS, which will then prompt the user to enter the serial number which is printed on the identification label on the back of the computer. 24