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Is RAM bus speed still a bottleneck


New member
I am buying a new computer to replace the one I have been using to run WRF for the past few years. I'm going to get the intel i9 12900 cpu which has 16 cores and 24 threads. I am still deciding if I should buy cheaper ddr4 memory with bus speed of 3600 MHz or ddr5 ram with higher bus speed. I've looked through the hardware post in tha FAQ and it is stated that the bus speed is important, but I have not found any info about what is enough.

Will higher bus speed always be better? Will I see significant speedup when using the fast ddr5 compared to the slower ddr4 with everything else unchanged? This is meant for a system that runs GFS 4 times daily almost 24/7.
So looking at the spec sheet for that cpu (Product Specifications)

According to the spec sheet the RAM has these specs.
Up to DDR5 4800 MT/s
Up to DDR4 3200 MT/s

For people who may read this in the future. Bus speed refers to how quickly the system bus can move data from one computer component to the other. The faster the bus, the more data it can move within a given amount of time. So the higher DDR5 ram will move more data between the hard drive and ram quicker.

What's also important for WRF is the amount of RAM and the type of hard drive you are using.
If you could get say 64GB or 128GB of DDR4 ram cheaper then 32 GB of DDR5 RAM then the bus speed should be negatable. This is because the WRF will have more RAM to utilize for large runs.

For Hard Drives, A standard HDD will read and write at typically 80MB/s to 160MB/s, but an SSD reads and writes at between 200MB/s to 550MB/s. So by having a SSD you use a slower bus speed for RAM and won't get a bottleneck at the hard drive.

Personally, my current desktop has this setup and runs the WRF pretty fast.

CPU: Processor Intel(R) Core(TM) i7-10700 CPU @ 2.90GHz, 2901 Mhz, 8 Core(s), 16 Logical Processor(s)
RAM: 64GB of DDR4 at 3200 MT/s
Hard Drive: SSD

Again this is just my personal option and I'm not an employee of NCAR. @kwerner @Ming Chen may have more information then I do.