When a computer is booted (started), serial presence detect (SPD) is information stored in an electrically erasable programmable read-only memory (EEPROM) chip on a synchronous dynamic random access memory (SDRAM) memory module that tells the basic input/output system (BIOS) the module's size, data width, speed, and voltage. The BIOS uses this information to configure the memory properly for maximum reliability and performance. If a memory module does not have SPD, the BIOS assumes the memory module's information. With some memory, this does not cause problems. But SDRAM memory has to have SPD or the computer may not boot at all. If it does boot, the assumed information may cause fatal exception errors.
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