Question: What does SPD stand for and what does it do?

Read our answer below:

Whenever you see SPD referred to in conjunction with a computer memory module it stands for Serial Presence Detect and is small amount of grouped data stored on the module to assist its detection and configuration once a system is turned on. SPD was first introduced when SDRAM came into use (circa 1996) replacing the older and less extensive PPD (Parallel Presence Detect) specification.


The laptop memory modules you insert into your laptop in the form of SODIMM's being the full technical name must be detected by your system and properly configured before they can be used. In order to do this, your laptop's BIOS reads the SPD data and compares it to the memory controller's capabilities prior to determining the best setup. In the case of installing two or more SODIMM's with varying frequencies, this process will also result in your system running at the speed of the slower SODIMM(s) so as to not cause instability. A BIOS that has been correctly implemented will always endeavor to run the system's memory at the highest speed supported both by the SODIMM's installed and that of the present memory controller, regardless whether the latter is found in a separate chipset to the main processor, or part of the processor die itself.


SPD stores various data necessary in performing the above, this includes supported profiles, which in turn contain data relating to the supported frequency, timings and voltage. Additional data will include the manufacturer's name and module model number.


For best performance and the least potential for rare but nevertheless possible compatibility issues it is advised to buy your laptop memory upgrade at the same time thus consequently keeping all the modules you intend on installing identical.


Learn more about the technicalities behind laptop memory in part 2 of the Laptop Memory Upgrades Guide and/or the different types of laptop memory in part 3 of the Laptop Memory Upgrades Guide.


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