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The Lewisburg Chipset
Lewisburg Platform Controller Hub
The C620-series "Lewisburg" chipset replaces Intel's previous-gen C610-series "Wellsburg" PCH. Lewisburg adds several improvements, such as four additional SATA 6Gb/s and USB 3.0 ports. It features a DMI 3.0 interface, which is similar to a PCIe link between the processor and chipset. That's a nice doubling of throughput compared to C610's 2 GB/s DMI 2.0. The chipset also adds 12 additional PCIe 3.0 lanes and supports up to 25 HSIO (High Speed I/O) lanes.
A new CPU uplink option can provide eight and/or 16 PCIe lanes directly to the processor (separate from DMI).
Perhaps most important, Intel now has chipset options with a built-in X722 Ethernet controller that provides up to 4x10Gb/1Gb ports supporting iWARP RDMA and network virtualization offloads. There are also QuickAssist hardware offload accelerators that augment cryptography and compression/decompression performance. Notably, these additions don't consume DMI bandwidth. Instead, they utilize the CPU uplink to populate lanes connected directly to the processor. The x8 and x16 uplink options support a number of routing schemes, as outlined in the Lewisburg Deployment Configurations slide.
Vendors can configure a maximum of one PCH per CPU socket, but rarely extend beyond four per motherboard (even in eight-socket systems). Multiple PCHs increase I/O and accelerator capabilities and also allow the system to survive a chipset failure via failover.
There are several 14nm chipset options that range from a 15W TDP to 26W. Interestingly, the LBG-L and LBG-T hubs offer the same features, only one has a lower TDP. We suspect these power-optimized PCHs are manufactured using a 14nm+ process. We do know they cost more.
Integrated 10Gb Ethernet will likely enjoy quite a bit of support from enterprise customers. Intel claims the PCH-based approach results in 25% less power consumption than PCIe add-in cards. iWARP RDMA support, which bypasses the OS and kernel to reduce CPU utilization and network latency, is an enticing addition. Notably, Omni-Path uses RDMA, so it fits into the Intel's comprehensive networking approach.
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