Question: Can I go ahead and buy PC3-14900 DDR3 SODIMM's for my laptop if it only requires PC3-8500 DDR3 SODIMM's?

Read our answer below:

Before we answer this question let's first make sure that everyone knows what is meant by PC3-14900 DDR3. This is an alternative name given to DDR3 memory that meets the requirements to run at an effective speed of 1866MHz. Sometimes such memory modules might be also referenced as DDR3-1866, which perhaps is easier to contemplate. The latter's 1866 refers to the effective memory frequency of these modules while 14900 is actually the memory bandwidth measured in Megabytes/second, commonly denoted as MB/s.

With that out of the way let’s proceed with answering the question. Unfortunately the answer is "it depends" and so requires a little more explaining. All modern SODIMM's feature a SPD (Serial Presence Detect) chip located on them that stores configuration data for that particular SODIMM such as timings and voltage. Each time you turn on your laptop, it's BIOS (or UEFI as it is known in select DDR3 memory based laptops and eventually all future models) checks the SPD of each installed SODIMM to setup the memory sub-system.

Memory manufacturers usually write SPD profiles for three different operating frequencies, for example a PC3-10600 SODIMM would usually contain SPD data for PC3-6400, PC3-8500 and PC3-10600 operation, this is to allow the same SODIMM to function in a wide range of laptops, in which case the corresponding memory controllers support PC3-6400, PC3-8500 and/or PC3-10600 frequencies. Consequently, a laptop that only supports PC3-8500 speeds but which has PC3-10600 SODIMM's installed would still work "out of the box". The SPD profiles are there to permit backwards compatibility, and also (as an example) allow manufacturers the freedom to halt manufacturing PC3-8500 DDR3 SODIMM’s if most sales become generated through PC3-10600 DDR3 SODIMM’s.

Since most memory manufacturers usually write SPD profiles for three different operating frequencies, it is unlikely for a PC3-14900 SODIMM to include a PC3-8500 base profile. In the worst case, if you install a PC3-14900 SODIMM(s) into a PC3-8500 only laptop then it may not even start. In the opposite case, such laptops may boot-up providing their BIOS have been programmed accordingly. To be on the safe side it pays to check what SPD profiles the SODIMM's you wish to install contain, or skip buying the most high-end enthusiast (thus most expensive!) SODIMM's in favour of more mainstream SODIMM's, with PC3-10600 SODIMM's being a good example.

Examples of PC3-14900 SODIMM's that do not contain a SPD profile for PC3-8500 operation include Kingston's PnP HyperX KHX1866C11S3P1K2/4G and KHX1866C11S3P1K2/8G memory kits.

Learn more about laptop memory modules in part 3 of the Laptop Memory Upgrades Guide

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