The ATMEL AT24RF08 (24RF08 for shorts) is a 8KiB serial access EEPROM with an RFID interface. Its serial interface is similar to that of the AT24C08 EEPROM, and it is better described in the AT24C08 datasheet.
Serial interface access to the EEPROM is available through the I2C bus on some ThinkPads, at I2C addresses 0x54 - 0x57 with an additional "access protection page" at address 0x5c.
An important difference to the 24C08 is, that burst writes over page boundaries WRAP AROUND to the beginning of the same page, instead of continuing in the next page.
Older Thinkpads suffered from accidental writes to this EEPROM by the device discovery routines in old lm_sensors implementations, resulting in a corrupted CMOS checksum ("CRC2 Error") as described in the problem with lm-sensors page.
The RF interface is not used on the ThinkPads, but the EEPROM also has a memory protection map, which the BIOS uses to verify the existence of the 24RF08 Part (otherwise it could be replaced with the 24C08 part). Note that this means the EEPROM suffers at least two write cycles every boot (unprotect/protect).
ThinkPads store critical information on this EEPROM, including the BIOS admin password. Editing this EEPROM bypassing the BIOS requires hardware hacking to access the chip's serial interace directly, however. It also requires special programs to access the chip's serial interface and decode the password. The procedure is detailed in Recovering BIOS Passwords.