RAM use question

[scole of TSBT]

If an application needs 256GB RAM and a system has a multi CPU mobo...
1. If you have a dual CPU mobo but only 1 CPU installed, can the RAM slots for the 2nd CPU be utilized?
2. If not, then if it has 2 CPUs installed but the app only uses 1 core, will the app be able to use the RAM in the 2nd CPU slots?

[Bryan]

1. No, the memory of the 2nd CPU (not present) is accessed through the CPUs QPI buses.

2. Yes, IIRC that was one of the scenarios described when I was investigating NUMA. NUMA tries to tie memory to the local processor but if it needs more it will map memory installed on the 2nd CPU.

Of course I could be wrong on both counts :D

[Haunted Forest]

If an application needs 256GB RAM and a system has a multi CPU mobo...
1. If you have a dual CPU mobo but only 1 CPU installed, can the RAM slots for the 2nd CPU be utilized?
2. If not, then if it has 2 CPUs installed but the app only uses 1 core, will the app be able to use the RAM in the 2nd CPU slots?

I think the slots for the 2nd cpu need the cpu, and yes the system can use all the system ram. if you download the motherboard manual it should explain more.

[Mumps]

Bryan is correct on both counts. The QPI on the processors is also used to connect the processors together, so if one processor wants to access the RAM controlled by the other one, they can work together on that. :)

[MindCrime]

I want to say that back in the day you might have gotten away with this but probably not doable. IIRC the memory controller was on the northbridge or maybe seperate entirely. This is a cloudy recollection but in the days of FSB I believe it was kind of run seperately in the eyes of the mobo. Now-a-days both AMD and Intel memory controller is on the CPU. All of which doesn't really matter cause you're talking about 256gb of ram which would obviously have to be newer.

What app needs 256gb?

[scole of TSBT]

What app needs 256gb?I don't know the actual name. On another forum a member said his son ran simulation software that required 256GB RAM and was asking for advice on configurations.