OK, I know that this is an old post but for information's sake. After doing some testing with 3200MHz and 3000MHz DIMMs in a 7550, it looks like there is some weird/wacky block that Dell have put into the BIOS controlling RAM speeds. I have tried various BIOS revisions (currently on the latest) and the block, AFAIK, is still in place. Contacting Dell about this (admittedly now several years ago) shed no more light on the subject. They were unable to help at all (had trouble understanding what a BIOS is)- sadly enough since it was a new laptop at the time.
If you have 3200MHz memory (non ECC), the maximum amount that the machine will handle is 96GB. This is with any of the slots populated. However, the key slot I found was slot 3. It seems that something is tied into that particular slot for some reason or other. Add a DIMM to that slot and you will NOT be able to run 128GB memory at all using 3200MHz DIMMs. Remove the DIMM from that slot (to go to 96GB) and things work fine. I would suggest NOT to run 3200MHz since if you are only using 3 DIMMs then you won't be taking advantage of the speed that comes with memory interleaving (akin to running stripped hard disks), which requires memory DIMM pairs.
If you have 3000MHz memory (non ECC), the maximum amount that the machine will handle is 128GB! This is with all slots populated. I managed to find some Kingston memory at that speed (took a bit of digging - annoyingly I had to return the 3200MHz memory) and it works perfectly fine.
As a side note, I am not sure as to how well the cooling is being done since once you drop in 128GB, the fans definitely run a LOT more than usual - and this is over the long term as well (have had the laptop for several years now). I have a sneaking suspicion that someone at Dell decided to limit the memory to 3000MHz DIMMs only to keep the temperatures under control. For example, if you drop in 3 nvme drives then things will definitely run hot. I have had to remove one of the drives in my setup to make sure that the fans (though they are still on and audible) aren't max'ing out constantly.
Hopefully with the newer Dell versions of the 7k series laptops address these issues. I would expect that they should do considering the amount of time that has past...
DELL-Cares
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November 8th, 2021 01:00
128GB 4x32GB 3200 MHz ram is not validated. See page 17 in the online Precision 7750 Setup and Specifications PDF.
Validated =
128GB, 4x32GB, DDR4, 2666 MHz, ECC
128GB, 4x32GB, DDR4, 2933 MHz, ECC
128GB, 4x32GB, DDR4, 2933 MHz, Non-ECC
TEDER
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April 12th, 2024 23:38
OK, I know that this is an old post but for information's sake. After doing some testing with 3200MHz and 3000MHz DIMMs in a 7550, it looks like there is some weird/wacky block that Dell have put into the BIOS controlling RAM speeds. I have tried various BIOS revisions (currently on the latest) and the block, AFAIK, is still in place. Contacting Dell about this (admittedly now several years ago) shed no more light on the subject. They were unable to help at all (had trouble understanding what a BIOS is)- sadly enough since it was a new laptop at the time.
If you have 3200MHz memory (non ECC), the maximum amount that the machine will handle is 96GB. This is with any of the slots populated. However, the key slot I found was slot 3. It seems that something is tied into that particular slot for some reason or other. Add a DIMM to that slot and you will NOT be able to run 128GB memory at all using 3200MHz DIMMs. Remove the DIMM from that slot (to go to 96GB) and things work fine. I would suggest NOT to run 3200MHz since if you are only using 3 DIMMs then you won't be taking advantage of the speed that comes with memory interleaving (akin to running stripped hard disks), which requires memory DIMM pairs.
If you have 3000MHz memory (non ECC), the maximum amount that the machine will handle is 128GB! This is with all slots populated. I managed to find some Kingston memory at that speed (took a bit of digging - annoyingly I had to return the 3200MHz memory) and it works perfectly fine.
As a side note, I am not sure as to how well the cooling is being done since once you drop in 128GB, the fans definitely run a LOT more than usual - and this is over the long term as well (have had the laptop for several years now). I have a sneaking suspicion that someone at Dell decided to limit the memory to 3000MHz DIMMs only to keep the temperatures under control. For example, if you drop in 3 nvme drives then things will definitely run hot. I have had to remove one of the drives in my setup to make sure that the fans (though they are still on and audible) aren't max'ing out constantly.
Hopefully with the newer Dell versions of the 7k series laptops address these issues. I would expect that they should do considering the amount of time that has past...