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Intel's 100 Series Platforms Feature Less Connectivity Than You Might Expect

In Intel's latest 100 Series chipsets, the company promised an impressive increase in the connectivity of its mainstream platform. USB 3.0 support improved, and the aging PCI-E 2.0 lanes coming from the chipset were replaced by a large number of PCI-E 3.0 lanes. These improvements sounded great when Intel originally showed us the series, but now we have found out the chipset isn't capable of offering everything we expected.

Following The Trail Of Breadcrumbs

In the most feature-rich 100 series chipset, the Z170, Intel specified that the platform would provide 10 USB 3.0 ports, 6 SATA 3.0 connections and as many as 20 PCI-E 3.0 lanes. Intel also listed a new feature: HSIO lanes (High-Speed I/O lanes). Initially, we knew that the PCI-E 3.0 lanes and HSIO were related, with PCI-E 3.0 lanes essentially being leftover HSIO lanes. But we didn't know that the SATA, USB 3.0, and gigabit Internet connection ran through these HSIO lanes, too.

Every SATA and USB 3.0 connection or port consumes an entire HSIO lane, as does each PCI-E and gigabit LAN connection. When all the SATA, USB 3.0 ports and LAN are used, there are only nine HSIO lanes remaining, which means that at most, only nine PCI-E lanes can be configured. But if the chipset can't support the full number of PCI-E lanes, then why did Intel say it can?

Explaining The Magic

It turns out that the connectivity specs Intel reported on its 100 series chipsets are just the max supported connections. For example, Z170 supports as many as 10 USB 3.0 ports, and 6 HSIO lanes are permanently configured as 6 USB 3.0 connections. If an OEM wants more, they can configure an additional four USB 3.0 ports, but this will consume the four HSIO lanes typically allocated to PCI-E lanes one through four.

Intel 100 Series Consumer Chipsets
CPU PCI-E 3.0 Config Support1 x 162 x 81 x 8 + 2 x 41 x 161 x 16
I/O Port FlexibilityYesYesNo
Maximum HSIO Lanes262214
Max Chipset PCI-E Support20 PCI-E 3.0 Lanes16 PCI-E 3.0 Lanes6 PCI-E 2.0 Lanes
Max PCI-E Support WhenAll SATA/USB 3.0/ and GbE Used975
USB Support (USB 3.0)14 (10)14 (8)10 (4)
SATA 3.0 Ports664

Similarly, none of the SATA ports are configured by default and can be configured onto various HSIO lanes, but this too will reduce the number of PCI-E lanes available. Things get worse when you look at PCI-E storage devices, which consume four PCI-E lanes and can be configured only in one of three ways. A PCi-E storage device can be connected to HSIO lanes 15-18, 19-22, or 23-26; however, they cannot be connected to any other group of 4 HSIO lanes.

The first PCI-E Storage Device can be configured without much issue, but enabling a second PCI-E storage device will also knock out at least two SATA ports.

On the PCI-E side of things, although PCI-E 3.0 provides significantly more bandwidth than the older PCI-E 2.0 standard, Intel has limited the use of these lanes to either x1, x2, or x4 configurations. This is likely to compensate for the very limited DMI 3.0 connection running between the CPU and the PCH, which is only capable of roughly 4 GB/s of bi-directional bandwidth. That is the same bandwidth that four PCI-E 3.0 lanes would have, and as such, the PCH isn't capable of feeding devices running at more than a PCI-E 3.0 x4 connection.

Intel 100 Series Business Chipsets
Maximum HSIO Lanes262018
USB Support (USB 3.0)14 (10)14 (8)12 (6)
SATA 3.0 Ports666
Chipset PCI-E Lanes20 PCI-E 3.010 PCI-E 3.08 PCI-E 3.0
Max PCI-E Support WhenAll SATA/USB 3.0/ and GbE Used955

We asked Intel if this limited bandwidth would negatively impact performance on the platform, and an Intel representative told us that it is unlikely that a sufficient number of devices connected to the PCH would be in use at the same time to saturate the connection.

Are We In The Oven Or Eating The House Made Of Candy?

To be fair, Intel created the HSIO system in an attempt to give OEMs broader control when configuring their motherboards, and the company has succeeded in that goal. However, the problem with this setup is that it gives users the impression that the chipset is capable of much more than it actually is, and that may disappoint some customers.

OEMs could take advantage of third-party controllers in order to partially overcome these issues, adding more SATA or USB 3.0 ports, but that will raise the overall cost of the motherboards and will result in less performance because of the limited bandwidth. In the end, users are getting less in these chipsets than we originally expected, but with plenty of USB and SATA ports available, it is hard to say how big of a problem this will be. Are we getting less than we paid for, or are we still in for a sweet experience?

Update, 9/30/15, 4:30pm PT: Clarified the way in which PCI-E storage devices are configured.

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