RAM slots 4 and 8 stuck at 1066MHz! WHA?

echoout

macrumors 6502a
Original poster
Aug 15, 2007
600
16
Austin, Texas
Hey folks, my pitiful old 2009 5,1 recently got a RAM upgrade from 4 x Corsair XMS3 8GB (1x8GB) DDR3 1333 MHz (PC3 10666) to filling the final 4 slots with more of the same. No matter what order I fill the slots, 4 and 8 show as running at 1066MHz.

Am I missing something obvious? You see my specs in my signature.
 

Spacedust

macrumors 6502a
May 24, 2009
936
95
Hey folks, my pitiful old 2009 5,1 recently got a RAM upgrade from 4 x Corsair XMS3 8GB (1x8GB) DDR3 1333 MHz (PC3 10666) to filling the final 4 slots with more of the same. No matter what order I fill the slots, 4 and 8 show as running at 1066MHz.

Am I missing something obvious? You see my specs in my signature.
So 2009 or flashed 4,1 to 5,1 ?

If flashed 4,1 to 5,1 you won't get 1333 until you replace CPU to 6-core models.
 

flowrider

macrumors 603
Nov 23, 2012
6,034
2,274
If flashed 4,1 to 5,1 you won't get 1333 until you replace CPU to 6-core models.
Not correct - The faster 4 core CPUs, will handle 1333MHz RAM. All 4 core from the X5550 to W5590 will run at 1333MHz.

However, I am confused by the OPs statement. Is your RAM showing different speeds for different slots?

Lou
 

echoout

macrumors 6502a
Original poster
Aug 15, 2007
600
16
Austin, Texas
Like my signature says, flashed to 5,1, using dual 6-core CPUs.

Slots 4 and 8 are showing as 1066MHz regardless of RAM configuration. All other slots show 1333MHz, regardless of configuration.
 

echoout

macrumors 6502a
Original poster
Aug 15, 2007
600
16
Austin, Texas
Just found this tidbit. Any insight?

"Dual-processor model

Slot 1: Memory Channel 1, Processor 1
Slot 2: Memory Channel 2, Processor 1
Slots 3 & 4: Memory Channel 3, Processor 1
Slot 5: Memory Channel 1, Processor 2
Slot 6: Memory Channel 2, Processor 2
Slots 7 & 8: Memory Channel 3, Processor 2
Slots 3 and 4, as well as slots 7 and 8, share a memory channel. The best memory performance is achieved when slot 4 (single-processor model) or slots 4 and 8 (dual-processor model) aren’t occupied. By not populating the second of the paired memory slots, you allow each memory module to connect to its own dedicated memory channel.

If you do choose to populate the last memory slots, you may reduce optimum memory performance, but only when memory in the shared slots is being accessed."
 

echoout

macrumors 6502a
Original poster
Aug 15, 2007
600
16
Austin, Texas
Okay, I ran Geekbench 3 in 64 bit mode with and without Slots 4 and 8 occupied.

Slots 4 and 8 empty (48GB):
Geekbench Overall Multi-Core Score = 30,149
Memory Multi-Core Score = 4616

Slots 4 and 8 occupied (64GB):
Geekbench Overall Multi-Core Score = 30,188
Memory Multi-Core Score = 4461

So not a ton of difference either way. Weird.
 
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