Memory DIMMs have a small flash memory chip (EEPROM) on them, containing an important descriptor table called the Serial Presence Detect (SPD). This data tells the system the size, speed, timings, operating voltage, manufacturer, part number, overclocking profiles, and all sorts of other information about each DIMM. The SPD chip is accessed using the SMBus protocol, which is based on I2C.
Tools such as CPU-Z, RAMMon, and RW Everything can be used to read the SPD data by talking to the flash chip over a...