Serial Presence Detect (SPD)
Definition - What does Serial Presence Detect (SPD) mean?
Serial presence detect (SPD) is information stored on an EEPROM chip when a computer is booted. It is located on an SDRAM memory module and communicates to the BIOS the module size, data width, speed and voltage, which are used to configure the module memory controller for maximum reliability and performance.
Techopedia explains Serial Presence Detect (SPD)
Parallel presence detect (PPD) data was used in earlier 72-pin SIMMs. However, the standard changed to SPD with the later model 168-pin DIMM. SPD encodes much more information.