With the Intel Core Ultra 7/9 200 series laptop processors the DDR5 SODIMM specification has changed slightly as it now supports CSODIMM 6400MT/s DDR5 memory modules for anything above 5600MT/s. This applies to all the laptop processors in this series, H or HX (255, 265, 275, 285).
Note (at the time of writing) CSODIMM is currently in limited production due to being quite recent and latency in this form factor is around CL 52 @6400MT/s but given time there will be improvements with gaming edition CSODIMM / low latency variants.
It’s all about signal integrity
CSODIMM is DDR5 SODIMM with an additional chip on the I/O side to re-transmit the data from the DRAM IC to the memory controller. This is done to improve signal quality as the higher frequency operation, 6400MT/s or above is more prone to interference (noise, EMI/RFI). The extra chip, clock re-driver means the data signal / integrity is maintained so it remains functional at the higher frequencies. This is also why regular 6400MT/s DDR5 memory modules work for some and not others whereas a CSODIMM module will not have this problem.
The above is beneficial to all gaming laptops using the following Intel processors, 265HX, 275HX, 285HX whether it be from ASUS, Gigabyte, XMG, DELL, Lenovo, MSI, ACER… the CPU is what defines memory functionality including maximum supported memory.
However for some reason laptop vendors are not always making this clear on their product specs, some are even quite confusing with different descriptions and specs on the same page for the same product so refer to Intel if in doubt. They follow the JEDEC standard for DDR5 which is currently clock driver modules for 6400MT/s or above.
