Citrix answers VMware on virtual desktop density – UPDATED

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At the end of January VMware revealed that is working to increase its virtual machines density up to 16 VMs per core, mostly for VDI environments. That is twice the average amount of VMs that customers seems able to accommodate today, and VMware suggested that this record depends on new Intel Xeon 5500 (codename Nehalem) CPUs.

Anyway, that number came out during an interview, with no additional details, so there’s a lot of analysis to do before getting excited.
Nonetheless, the claim generated much interest (and skepticism), at the point that Citrix decided to answer.

The company says that it can cram into a single physical server up to 125 virtual desktops (and 500 hosted shared desktops and 5,000 local streamed desktops) with XenDesktop 4.0 and the Xeon 5500 CPUs.

Now, even if we know that Nehalem CPUs have four cores each, Citrix is not saying how many CPUs are powering this single server. We assume it’s a two socket system, which would mean 16 VMs per core.
The difference is that VMware seems to expect such density in future versions of View, while Citrix is claiming that it can deliver it today.

Can the two companies qualify these statements please?

Update: Citrix promptly answers with details: 130 Windows XP desktops on a 72GB, dual socket, quad-core Intel Xeon x5570 (codename Nehalem) host, running XenServer 5.5 and XenDesktop 4.0.

Citrix measured the density using the independent benchmark framework called Project Virtual Reality Check, which already raised a lot of attention exactly one year ago, when it was used to compare performance of VMware ESX, Citrix XenServer and Microsoft Hyper-V for Terminal Services and VDI workloads.