Question: Can I mix memory modules with different CAS latency?

Read our answer below:

The short answer is yes but your laptop will suffer a small (up to 5%) performance hit in most cases. The longer answer to this is that all moderm (SDRAM or newer) laptop memory modules feature timings data configured in what's known as a Serial Presence Detect (SPD) chip, which is set in such a way to comply with JEDEC memory standards. The result is that upon installation of two memory modules of varying CAS latency, the onboard laptop's BIOS checks and reads this SPD data, and configures the memory accordingly. In practise this means the slower memory module will always take priority hence the faster memory module will be forced to run at a slightly slower set of timings (of which CAS might be one of them)


An easy means to buying two laptop memory modules that have the same CAS latency (or simply SPD data) is to follow part 5 of the Laptop Memory Upgrades Guide.


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