This mixed memory configuration worked fine for me in two different T5500s. Of course YMMV because this is not a "Supported Memory Configurations." That means that during the release cycle of these machines Dell did not test for this config to work in all situations and thus compatibility might be a hit-or-miss kinda thing in some situations.
The tests below show that for my 2 T5500s this memory config ran without error and at the same memory speed at which each T5500 normally runs. Neither of these two T5500s run RAM at the maximum rate of 1333 MHz because the CPUs that they have in them won't support that. One CPU supports 1066 MHz RAM and the other supports 800 MHz RAM. If this test would have been done with a Xeon X5550 or better (1333 MHz support) then MAYBE some slight RAM speed slowdown might have appeared ... who knows.
The tests below were done with the Samsung M393B5673EH1-CH9 2 GB DIMMs (PC3-10600R/DDR3-1333) I mentioned in the 1st post. For the 4 GB DIMMs I used low voltage Samsung M393B5170FH0-YH9 DIMMs (PC3L-10600R/DDR3-1333) because that is what I have on hand. I was previously unaware that you could mix normal and low voltage DIMMs, but I found a post about that on this board. With the T5500/T7500 you can mix (YMMV) as long as you keep them in different banks/groups.
On a T5500 the triple channel memory banks/groups are (one per line): DIMM1/DIMM2/DIMM3 DIMM4/DIMM5/DIMM6 the 3 riser card DIMM slots (if you have a 2nd CPU)
Both of the tests below are with 4 GB DIMMs in DIMM1/DIMM2/DIMM3 and 2 GB DIMMs in DIMM4/DIMM5/DIMM6 and no riser card/2nd CPU installed. All of the DIMMs are dual rank (2Rx4/2Rx8). It has been suggested to me by someone I respect that mixing DIMMs with different ranks is usually not such a hot idea (YMMV). In a T5500 if you have mixed sized DIMMs then put the larger DIMMs on the riser card if you have one else put them in DIMM1/DIMM2/DIMM3. In each memory bank/group you want to have the same kind of RAM. Doing everything in threes is optimal and highly suggested.
The first machine that I tried was a 2011 T5500 (mobo 0CRH6C) with a Xeon E5504 CPU. It appears that all CPUS E5506 or lower will only support 800 MHz memory and the E5504 is in this bucket. That means that a faster DIMM should "clock down" to 800 MHz. I did a 24 hr. Memtest86+ v5 test of the mixed config of 4 GB/2 GB DIMMs without any errors. The BIOS set the RAM to 800 MHz = PC3-6400/DDR3-800 speeds. This is bit of a speed loss, but the problem here is with the CPU, not the RAM.
The second machine that I tried was a 2009 T5500 (mobo 0CRH6C) and the CPU was a Xeon E5640. It appears that CPUS E5550 or higher will support 1333 MHz memory and CPUs E5520 or higher support 1066 MHz memory. It appears that the E5640 is in the 2nd bucket (1066 MHz support).
I did a 12 hr. Memtest86+ v5 test of the mixed config of 4 GB/2 GB DIMMs without any errors. The BIOS set the RAM to 1066 MHz = PC3-8500/DDR3-1066. Again, the slowdown was because of the CPU.
The stickers on the 2 mobos both say 0CRH6C, but the numbers after that are a bit different, so there might be some slight variation there. The 2009 T5500 has the latest BIOS and the 2011 still has an early BIOS (A06?).
About running memory at slightly slower speeds ... I suspect that if you are using a computer that has had the memory slowed down a bit that you would have a hard time "feeling the difference" because of the fact that main memory location that you want at any given time is likely already in the L1/L2/L3 cache on the CPU.
Benchmarks can certainly show somewhat of a difference because of RAM speed slowdown, but if you are clicking around on a computer and it is 5% faster or slower it's all gonna feel the same.
Any comments/observations are quite welcome, particularly about what the supported memory speeds are for the CPUs that the T5500 can take (also T7500).
I notice that in the very recent thread started by user claytonb titled "Memory Configuration in Precision T5500" that he has a very similar memory config and it works for him.
It appears that I cannot link to that post so a screwed up link follows.
mrpetedell
9 Posts
0
June 10th, 2015 12:00
I ran two tests and the results are ...
This mixed memory configuration worked fine for me in two different T5500s. Of course YMMV because this is not a "Supported Memory Configurations." That means that during the release cycle of these machines Dell did not test for this config to work in all situations and thus compatibility might be a hit-or-miss kinda thing in some situations.
The tests below show that for my 2 T5500s this memory config ran without error and at the same memory speed at which each T5500 normally runs. Neither of these two T5500s run RAM at the maximum rate of 1333 MHz because the CPUs that they have in them won't support that. One CPU supports 1066 MHz RAM and the other supports 800 MHz RAM. If this test would have been done with a Xeon X5550 or better (1333 MHz support) then MAYBE some slight RAM speed slowdown might have appeared ... who knows.
The tests below were done with the Samsung M393B5673EH1-CH9 2 GB DIMMs (PC3-10600R/DDR3-1333) I mentioned in the 1st post. For the 4 GB DIMMs I used low voltage Samsung M393B5170FH0-YH9 DIMMs (PC3L-10600R/DDR3-1333) because that is what I have on hand. I was previously unaware that you could mix normal and low voltage DIMMs, but I found a post about that on this board. With the T5500/T7500 you can mix (YMMV) as long as you keep them in different banks/groups.
On a T5500 the triple channel memory banks/groups are (one per line):
DIMM1/DIMM2/DIMM3
DIMM4/DIMM5/DIMM6
the 3 riser card DIMM slots (if you have a 2nd CPU)
Both of the tests below are with 4 GB DIMMs in DIMM1/DIMM2/DIMM3 and 2 GB DIMMs in DIMM4/DIMM5/DIMM6 and no riser card/2nd CPU installed. All of the DIMMs are dual rank (2Rx4/2Rx8). It has been suggested to me by someone I respect that mixing DIMMs with different ranks is usually not such a hot idea (YMMV). In a T5500 if you have mixed sized DIMMs then put the larger DIMMs on the riser card if you have one else put them in DIMM1/DIMM2/DIMM3. In each memory bank/group you want to have the same kind of RAM. Doing everything in threes is optimal and highly suggested.
The first machine that I tried was a 2011 T5500 (mobo 0CRH6C) with a Xeon E5504 CPU. It appears that all CPUS E5506 or lower will only support 800 MHz memory and the E5504 is in this bucket. That means that a faster DIMM should "clock down" to 800 MHz. I did a 24 hr. Memtest86+ v5 test of the mixed config of 4 GB/2 GB DIMMs without any errors. The BIOS set the RAM to 800 MHz = PC3-6400/DDR3-800 speeds. This is bit of a speed loss, but the problem here is with the CPU, not the RAM.
The second machine that I tried was a 2009 T5500 (mobo 0CRH6C) and the CPU was a Xeon E5640. It appears that CPUS E5550 or higher will support 1333 MHz memory and CPUs E5520 or higher support 1066 MHz memory. It appears that the E5640 is in the 2nd bucket (1066 MHz support).
I did a 12 hr. Memtest86+ v5 test of the mixed config of 4 GB/2 GB DIMMs without any errors. The BIOS set the RAM to 1066 MHz = PC3-8500/DDR3-1066. Again, the slowdown was because of the CPU.
The stickers on the 2 mobos both say 0CRH6C, but the numbers after that are a bit different, so there might be some slight variation there. The 2009 T5500 has the latest BIOS and the 2011 still has an early BIOS (A06?).
About running memory at slightly slower speeds ... I suspect that if you are using a computer that has had the memory slowed down a bit that you would have a hard time "feeling the difference" because of the fact that main memory location that you want at any given time is likely already in the L1/L2/L3 cache on the CPU.
Benchmarks can certainly show somewhat of a difference because of RAM speed slowdown, but if you are clicking around on a computer and it is 5% faster or slower it's all gonna feel the same.
Any comments/observations are quite welcome, particularly about what the supported memory speeds are for the CPUs that the T5500 can take (also T7500).
I notice that in the very recent thread started by user claytonb titled "Memory Configuration in Precision T5500" that he has a very similar memory config and it works for him.
It appears that I cannot link to that post so a screwed up link follows.
http://en.community.dell.com/
support-forums/desktop
/f/3514/t/19632835