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Double-speed next-gen version cements PCIe computing power

PCI Express has lasted more than a decade, and faster speeds should extend its longevity as a key enabler of computing power. Also coming: adaptations for the mobile market.

PCI Express 4.0 carries 16 gigabits of data per second per link; a collection of 16 links means aggregate bandwidth of 64 gigabytes per second.
PCI Express 4.0 carries 16 gigabits of data per second per link; a collection of 16 links means aggregate bandwidth of 64 gigabytes per second. PCI-SIG

A fourth generation of PCI Express is on the way, doubling data-transfer speeds over today's version of this key technology that wires up the internals of today's computers.

The new version -- which should help with higher-speed storage, data-hungry graphics chips, and lower-cost electronics -- is settling down. The computing companies defining PCIe 4.0 plan to release a new draft of the standard in the second half of 2014 as they hammer out just how it'll work.

PCI Express, or PCIe for short, is a high-speed data pathway inside computers used to connect devices like network cards and, more recently, high-speed storage drives. It's also a foundation of Intel's Thunderbolt technology for attaching external devices like storage arrays and docking stations. In other words, you may not have heard of it, but you use it all the time.

PCIe sends data over multiple electronic links called lanes, with computer engineers ganging together multiple lanes for higher transfer speeds. Today's third-generation version can transfer 8 gigabits per second on each lane, but PCIe 4.0 increases that to 16Gbps.

"This bit rate represents the optimum tradeoff between performance, manufacturability, cost, power, and compatibility," said the PCI Special Interest Group, a consortium of computing companies that oversees PCIe, on Wednesday at their PCI-SIG DevCon event.

PCIe 4.0 should cut costs. Although enabling faster data transfer is important, doubling speeds also can cut costs, because hardware designers who don't need to send more data can get by with fewer PCIe lanes or cover more uses with the same number. As PCIe takes over from today's SATA standard for connecting hard drives and SSDs, there will be new demand for PCIe connections.

Input-output interfaces come and go, but PCIe has shown remarkable longevity. PCI Express debuted in 2004 as an Intel technology called Arapahoe.

But computing has changed a lot in the last decade. PCIe is adapting with the times -- notably the mobile computing, where laptops need battery power and smartphones and tablets now are widely used.

The PCIe OcuLink connector could make this internal data-transfer technology into a rival for Intel's Thunderbolt.
The PCIe OcuLink connector could make this internal data-transfer technology into a rival for Intel's Thunderbolt. PCI-SIG

There, power consumption is a big deal, since nobody wants to shorten the battery life of mobile devices. PCIe 4.0 will use the same power as PCIe 3.0, the PCI-SIG said.

PCIe is branching out too, with a variation called M-PCIe. With it, PCIe data transfers take place over another physical interconnect that's used in mobile devices, the MIPI Alliance's M-Phy. M-Phy provides data connections in smartphone-size devices between various modules like videocameras, processors and radio-communication chips.

That'll extend PCIe's utility in ultralight laptops, tablets, and smartphones, the PCI-SIG said -- and M-PCIe is adapted for low-power situations.

Another mobile adaption that's on the way is called M.2, a new connector designed for hooking up solid-state drives (SSDs) and wireless network chips in slim devices like tablets and ultralight laptops. It works both with a low-profile connector or with directly soldering the electronics down.

PCIe has been remarkably successful, but it's had its failings too. One big one has been a years-old ambition to give PCIe a high-speed external port. The latest incarnation of this effort is called OcuLink, and the first version of the spec is almost done, with product adoption expected in the second half of 2014, the PCI-SIG said Wednesday.

OcuLink uses four 8Gbps links of PCIe 3.0, offering 32Gbps total data-transfer capacity. It's geared for devices like external storage arrays that can have a big appetite for data, for example as video editors work on high-resolution projects. It comes in both copper wire and fiber-optic versions.

But the PCI-SIG has a big competitor here: Intel's Thunderbolt. It already offers 40Gbps today, is built into all new Macs and some high-end Windows machines, and works with a variety of peripherals already.

Thunderbolt is based on PCIe, but importantly, it also accommodates the DisplayPort standard so high-resolution monitors can be connected to Thunderbolt ports too. That gives Thunderbolt useful flexibility.

And presumably Thunderbolt will be updated to handle PCIe 4.0 for even faster speeds later. That means that even if OcuLink doesn't catch on widely, PCIe will still ultimately win the war.