Memory performance - SiSoftware Sandra

Website: SiSoftware Sandra

Although the Xeon 5400-series CPUs were faster in many applications than the Opteron 2300-series CPUs, performance in some situations suffered because the Xeons used FB-DIMM memory. While FBDIMMs offer some advantages over ECC registered DDR2, such as the ability to support more memory channels and therefore a higher number of DIMMs, FB-DIMMs are surprisingly slow.

In addition, their AMB (Advanced Memory Buffer) chips run hot and consume a lot of power, so FB-DIMMs require active cooling. This means that a system with multiple 2300-series Opterons with ECC registered DDR2 is actually a better choice for many bandwidth intensive high-performance computing (HPC) applications than a system with multiple 5400-series Xeons.

When FB-DIMM was first launched, Intel made lots of bullish statements about the standard being the future of workstation/server memory. However, for Nehalem EP, Intel has quietly dropped FB-DIMM in favour of triple-channel ECC registered DDR3. Such DIMMs are not only a lot more power efficient than FB-DIMMs, they are also able to run at a much higher frequency (1,333MHz versus 800MHz).

With no AMB chip to slow down write operations, we were keen to see if memory bandwidth and latency were still an Achilles heel for the new Xeon 5500-series. We started by populating all four sockets of the Xeon X5482 test system with Crucial CT12872AF80E 800MHz FB-DIMMs, while the Xeon W5580 system was populated with six Crucial CT25672BB1339S 1,333MHz ECC registered DIMMs.

Unbuffered memory bandwidth

Memory latency

While the Xeon W5580 system still has less memory bandwidth than an Opteron system, its triple-channel DDR3 is a massive improvement over previous generation Xeon systems with FBDIMM memory. This huge increase in memory bandwidth is one reason why the Xeon W5580s are so incredibly fast in the HPC benchmarks. Clearly Intel made the right, albeit overdue, decision to replace FB-DIMM with ECC registered DDR3 for the Xeon 5500-series.


You can buy a 6GB (3 x 2GB DIMMs) set of Crucial CT3KIT25672BB1339 for £251.84 inc VAT from Crucial. You’ll need two such kits to provide each CPU with its own bank of memory.