amd DDR5 AM5 question: Ability to disable and enable DIMMS on the fly for either fast RAM or huge capacity when it's needed.

[Newbert]

AMD has a slower speed for their RAM when 4 DIMMS are installed and faster when only 2 DIMMS are installed. Would it theoretically be possible to disable 2 DIMMS dynamically (While the system is running and booted into OS.) when less RAM is being used and enable the other 2 DIMMS when massive amounts of RAM are required by the system? Thereby getting the benefits of a ton of RAM or fast clock speeds.

 

This is without removing the DIMM modules manually each time since that could be tedious, error prone, and potentially destructive if you're unlucky.

[Alex Atkin UK]

7 minutes ago, Newbert said:

AMD has a slower speed for their RAM when 4 DIMMS are installed and faster when only 2 DIMMS are installed. Would it theoretically be possible to disable 2 DIMMS dynamically (While the system is running and booted into OS.) when less RAM is being used and enable the other 2 DIMMS when massive amounts of RAM are required by the system? Thereby getting the benefits of a ton of RAM or fast clock speeds.

 

This is without removing the DIMM modules manually each time since that could be tedious, error prone, and potentially destructive if you're unlucky.

No, the RAM is hardwired to the CPU.

 

Is this because you need 128GB of RAM?  As 64GB can be installed with two sticks.

[RONOTHAN##]

8 minutes ago, Newbert said:

Would it theoretically be possible to disable 2 DIMMS dynamically (While the system is running and booted into OS.) when less RAM is being used and enable the other 2 DIMMS when massive amounts of RAM are required by the system?

No, changing the amount of RAM in a system and the RAM clock speed requires a memory retrain (assuming you're not doing funky stuff with the BCLK as that will cause instability). This just isn't possible.

 

The closest thing that might be possible is that some boards do have the ability to enable and disable DIMMs within the BIOS, so you could do this with a reboot. Problem is I'm not aware of any AM5 boards that have this ability, only a handful on Intel boards (and I mean handful, you can count on one hand the number of boards that have had this feature within the last ~15 years). 

 

 

Just get a pair of the 2x48GB sticks and run them, you should be able to get DDR5 6000 CL30 to work with the Hynix based DIMMs (the ones rated 6400 CL32 at this time) and very few people need more than 96GB of RAM on AM5. 

[Newbert]

On 10/6/2023 at 9:24 PM, RONOTHAN## said:

No, changing the amount of RAM in a system and the RAM clock speed requires a memory retrain (assuming you're not doing funky stuff with the BCLK as that will cause instability). This just isn't possible.

 

The closest thing that might be possible is that some boards do have the ability to enable and disable DIMMs within the BIOS, so you could do this with a reboot. Problem is I'm not aware of any AM5 boards that have this ability, only a handful on Intel boards (and I mean handful, you can count on one hand the number of boards that have had this feature within the last ~15 years). 

 

 

Just get a pair of the 2x48GB sticks and run them, you should be able to get DDR5 6000 CL30 to work with the Hynix based DIMMs (the ones rated 6400 CL32 at this time) and very few people need more than 96GB of RAM on AM5. 

That might be the best idea.

I was originally planning on jamming an entire 50GB virtual machine image inside of RAM and compiling software inside of it so that I don't 'starve' my CPU of stuff to work on. To make compile time a lot faster for large operating systems. So, my target was 192GB DDR5 initially.