E5 1620V2 qpi/dmi?

All modern Intel microprocessors use DMI 2.0 which provides 20Gbps of bandwidth using an 8b/10b coding scheme (which results in 20% overhead) for a total of 16Gbps of data, or 2GBps of data. It's only used to move data between the CPU and the PCH, which is mostly used for servicing network and storage.

In multi-socket systems the QPI links are used to communicate between the microprocessors themselves.

The exception to this is the first generation i7 900 series on the X58 platform in which QPI was used to connect the microprocessor to the Northbridge as the PCIe lanes hadn't been integrated onto the microprocessor itself yet.

The reason why the E5-1620v2 shows as having a 0GT QPI bus is that it is only uni-processor capable. It can only be used in a system with a single socket as the QPI bus is deactivated. The E5-1620v2 is the LGA2011 counterpart to the E3-1290v2 which uses the LGA1155 platform.

The E5-2630v2 has active QPI links as it can be placed in a dual-socket motherboard for a total of 12 active cores.

Here's an explanation of Intel's naming conventions.

The Ex prefix is a power marketing tool. E3 microprocessors are simple analogues to the mainstream desktop parts on the LGA1155/LGA1150 platforms. E5 microprocessors are the analogues to the LGA2011 platform that can be used in single, dual, or quad socket motherboards with between 4 and 12 cores per microprocessor package. E7 microprocessors are on steroids; they have up to 15 cores per microprocessor and can be used in dual, quad, and octal socket systems.

The first of the 4 numbers following the E series is the "wayness" of the microprocessor. This is the maximum number of other processors that it can communicate with in a multi-socket system. A 1000 series microprocessor is uni-socket only, 2000 series is dual-socket, 4000 series is quad-socket, and 8000 series is octal-socket. The following 3 numbers are a relative power scale with higher numbers indicating more cores, more cache, and higher frequency.

The "vx" suffix refers to the generation of the core architecture employed. v1 (absent suffix) is Sandybridge, v2 is Ivybridge, and v3 is the new Haswell microarchitecture.

Sandybridge based Xeon microprocessors have populated the E3 and E5 series, but there are no E7 based Sandybridge microprocessors, so no octal-socket systems. There are plans for E7 based Ivybridge microprocessors though by the looks of it. Haswell has just been released on the LGA1150 platform and thus has only E3-1000v3 series microprocessors. The E5 Haswell based microprocessors will come in the future so as of this moment there are no E5-2000v3 series microprocessors on the market.

If you want only a single socket system, go with either the E3-1290v2 or E5-1620v2 for four cores, or the E5-1650v2 for six cores. If you want a dual socket system with 12 cores, go with a pair of the E5-2630v2.

EDIT: All E3 series microprocessors have 16 PCIe lanes pulled directly from the CPU. Sandybridge E3s are PCIe 2.0 compliant, Ivybridge E3s are 3.0 compliant. All E5 series microprocessors have 40 PCIe lanes pulled directly from the CPU, both Sandybridge and Ivybridge based E5s are PCIe 3.0 compliant.

In the case of the E5-1620, QPI is used in lieu of the frontside bus, connecting the processor to the I/O hub. It does not use DMI.

QPI links can serve as interconnects between processors but also also connects the processor to the I/O hub. This is true for all E5-16*** and E5-14** processors.