Performance Benchmarks

This first generation of Nehalem processors has three channels per socket. When the number of DIMMs installed on all channels is the same, the peak memory bandwidth is achieved. If there are different numbers of DIMMs installed on the various channels, the memory bandwidth will be less.

The SiSoft Sandra benchmark is used to determine the memory bandwidth. The Cinebench benchmark is used to indicate the impact of the changes in memory bandwidth on a memory-intensive application. The benchmarks were performed under 64-bit Windows Vista SP1 with no other patches. The appropriate drivers for the motherboard were installed.

Do not confuse memory bandwidth with real-world application performance.

Once all the CPUs in a system are running with at least two channels, the difference in memory bandwidth usually has no impact on actual application performance. Vastly more important is having enough memory to eliminate paging, and to provide enough memory to cache file I/O.

Uni-Processor Benchmarks

When dealing with a Uni-Processor system, the bandwidth capabilities are rather limited. The processor clocks for the two tested processors are the same. The differences between them are the UnCore clock and the maximum memory clock. With more than three memory modules, both processors will run the memory at 533MHz. The types memory used in these benchmarks are:

• 533MHz DDR3 CAS-7 Unbuffered ECC Dual-Rank
• 666MHz DDR3 CAS-9 Unbuffered ECC Single-Rank
• 666MHz DDR3 CAS-9 Unbuffered ECC Dual-Rank

Notes:

(1) This memory is underclocked 666MHz DDR3 CAS-9 Unbuffered ECC Single-Rank, which runs at CAS-7.

Dual-Processor Benchmarks

With the exception of the 8-DIMM dual-channel test, the DIMMs were installed as evenly as possible between the two processors, and among the channels of each processor. The first set of benchmarks uses the E5520 processor. The types memory used in these benchmarks are:

• 533MHz DDR3 CAS-7 Unbuffered ECC Dual-Rank
• 666MHz DDR3 CAS-9 Unbuffered ECC Single-Rank

Notes:

(1) This memory is underclocked 666MHz DDR3 CAS-9 Unbuffered ECC Single-Rank, which runs at CAS-7.

This set of benchmarks uses the X5550 processor. The types memory used in these benchmarks are:

• 533MHz DDR3 CAS-7 Unbuffered ECC Dual-Rank
• 666MHz DDR3 CAS-9 Unbuffered ECC Single-Rank
• 666MHz DDR3 CAS-9 Unbuffered ECC Dual-Rank
• 666MHz DDR3 CAS-9 Registered ECC Dual-Rank

It can be seen that there's a significant difference in the memory bandwidth between 533MHz dual-rank memory and 666MHz dual-rank memory. It can also be seen that there's a similar difference in memory bandwidth between single-rank and dual-rank memory modules.