Intel Xeon 5500 series: 14 CPUs tested and compared
The Nehalem-based Xeons are a landmark release, with exceptional performance married to great power.
After much speculation and anticipation, Intel’s new 5500 Series Xeon processors have finally arrived - and judging by the number of new features and improvements on offer, the wait looks well worthwhile.
Codenamed Nehalem, Intel’s new micro-architecture represents the next step in its “tick-tock” design model, where the last phase was to introduce the Core architecture and then shrink it to 45nm.
Nehalem delivers the next “tock” phase, but it’s far more significant than that since it represents a sea change in processor design. Instead of presenting a one-size-fits-all solution, Nehalem effectively offers a set of building blocks.
This allows it to scale not only across different hardware, but also across different market sectors including mobile, desktop and server DP and MP applications.
We’ve already covered Intel’s Core i7 implementation (web ID: 131494), and now we look closer at the 5500 series “Gainestown” Xeon DP server processors. Tech specs
The new processors still use the 45nm manufacturing process, but the four cores are on a single die and share one chunk of L3 cache, which can be up to 8MB.
They use the same L1 cache as the existing Core technology, but have a lower latency 256KB L2 cache per core. The processors use a larger LGA1366 socket, and the main reason for the increase in size is the processors now incorporate an integrated memory controller and a link controller for Intel’s new QPI (Quick Path Interconnect).
You can wave goodbye to the trusty old FSB, which was used to create a backbone between the processors and the chipset’s memory controllers and I/O bus. It worked well enough, but it created a bottleneck since all system memory was in a single, shared location.
The QPI facilitates high-speed connections between processor and I/O controller. Each processor has its own dedicated memory, which it accesses via its integrated controller. It uses the QPI for fast access to the I/O controller, and the 5500 series Xeons also have a QPI link between dual-processor sockets.
The QPI operates at speeds of up to 25.6GB/sec or 6.4GT/sec (GigaTransfers/data transfers/operations per second).
It effectively allows all system memory to be no more than one hop away from any processor, and as QPI is point-to-point there’s none of the single bus contention in the FSB. If one processor needs to access the memory on the other processor, it can do so via QPI links.
Intel’s Turbo Boost technology uses the fact that most apps don’t scale to an arbitrary number of CPUs. A controller on the processor monitors the load and can power down a core if it isn’t being used. This creates thermal/power headroom, which can be passed on to the other cores and used to boost their speed.
The more cores that are powered down, the more boost is available to the active cores and frequencies are raised in bins, or 133MHz increments. For example, a 2.8GHz X5560 Xeon could be boosted to 3GHz with three or four active cores and up to 3.2GHz with one or two cores active.
As FSB leaves the building Intel now reacquaints us with Hyper-Threading, which allowed older Pentium and Xeon processors to simultaneously run two threads per core.
For Nehalem, this hasn’t changed in principle, but the larger cache and higher bandwidth means that – dependent on the application – it can realise a significant performance improvement for fully multithreaded apps.Virtual and memory enhancements
Support for server virtualisation is end-to-end, as you have Intel’s VT-x and VPID (virtual processor ID) in the processors, and these have been augmented with improvements to the EPTs (extended page tables).
Combined together these are capable of increasing VM performance and reducing latency for VM transitions.
Implemented in the new Tylersburg chipset, VT-d (directed I/O) supports DMA and device generated interrupt protection and remapping. The VT-c (connectivity) suite is aimed at end devices such as compliant 10GbE network adapters and includes VMDq (Virtual Machines Device Queue), which optimises networking performance for VMs.
More changes are evident in the memory department as the 5500 series supports only DDR3 memory, with speeds currently topping out at 1333MHz. Performance improvements can be had by installing them in packs of three per DIMM bank for triple-channel access, but you don’t have to.
You can choose between RDIMMS (registered) or UDIMMs (unregistered), but FBDIMMs aren’t supported. RDIMMs support three DIMMs per channel, whereas the cheaper UDIMMs support only two per channel but are more cost-effective where you’re not planning on using more than 4GB in a server.
Choosing a 5500 Xeon
When picking your new processors choose carefully, as there are significant differences across the 5500 family.
It starts with four entry-level models with the dual-core E5502 having a 4MB L3 cache, supporting 800MHz memory speeds, a QPI speed of 4.8GT/sec and not implementing Turbo Boost or Hyper-Threading.
The other three are quad-core, but have the same specifications.
Starting with the 2.26GHz L5520 and E5520, the next group of four processors supports memory speeds up to 1066MHz, has a QPI speed of 5.86GT/sec, and implements Turbo Boost and Hyper-Threading.
The X5500 models offer all available features, along with a QPI speed of 6.4GT/sec and supported memory speeds up to 1333MHz.
At the very top of the range sits the W5580, which has a 3.2GHz frequency, 130W power needs and a price to match. The other models to consider are the low-power versions, beginning with “L”.
The embedded L5508 consumes just 38W at most, but includes a mere two cores. The more mainstream choice is the L5520, which we tested in the Fujitsu Primergy.
See the full table of processors for an at-a-glance guide to pricing and specification.
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This Group Test appeared in the August, 2009 issue of PC & Tech Authority Magazine