[Beowulf] PCI Express takes on Thunderbolt

Eugen Leitl eugen at leitl.org
Thu Jun 23 13:00:59 PDT 2011


PCI Express takes on Thunderbolt

Rick Merritt

6/22/2011 6:06 PM EDT

The PCI Special Interest Group will launch an effort in July to create a
cabled version of PCI Express that will take on the Thunderbolt interconnect
developed by Intel.

SANTA CLARA, Calif. – The PCI Special Interest Group will launch an effort in
July to created a cabled version of PCI Express that will take on the
Thunderbolt interconnect developed by Intel and Apple. Backers suggest the
PCIe approach will be more open and more optimal than Thunderbolt for
delivering high throughput I/O to tablets and thin notebooks.

The new cable will be based on PCIe 3.0 which supports up to 8
GTransfers/second. It likely will support a maximum of four parallel lanes
for throughput up to 32 Gbits/s and distances no longer than three meters.

While initially focused on copper, the technology is expected to migrate to
higher speed copper and optical links. The road map likely leads to a 16 GT/s
version based on PCIe Gen4 in about four years as well as an optical version
for longer reach and/or higher data rates at some point.

The cable and connector itself are expected to be flatter than those of
Thunderbolt. The PCIe cable also will support power to peripherals at levels
likely less than 20W.

Details of the new standard will be defined by a working group now being
formed. The group is expected to deliver a standard system makers can
implement in products before June 2013.

The effort to write the spec could take nine to 18 months. The biggest part
of the work is expected to be defining technical requirements and a new

The new spec is aimed at consumer uses for desktop and mobile PCs and tablets
as well as their peripherals such as external storage devices. The PCI SIG
has a separate cable group, chartered in 2005, that has already delivered a
spec for the 2.5 and 5 GT/s versions PCIe 1.1 and 2.0, supporting distances
up to eight meters and aimed for use in servers and other data center

Representatives of the PCI SIG declined to comment in any way on Thunderbolt.
However, the initiative is clearly aimed at similar applications including
external disk and solid-state drives.

"This will help proliferate PCI Express into new business opportunities,"
said Al Yanes, president of the PCI SIG, declining to give examples of how it
will be used.

"Right now we see a need from our members," Yanes said, declining to comment
on Thunderbolt directly.

"There are solutions [like this] in the industry--Thunderbolt is one of them,
and some companies are doing own thing," he added.

Comparing PCIe cable, Thunderbolt

"The big issue here is proprietary versus industry standard," said Nathan
Brookwood, principal of market watcher Insight64 (Saratoga, Calif.). "It's
not clear third parties will have access to Thunderbolt on the same basis
they get access to PCI Express," he said.

Indeed, one chip maker on the show floor of the annual PCI SIG developers
conference here said his company is working on a Thunderbolt design. However,
the gating item to getting it completed is getting access to the technology
from Intel, he said.

The motivation for the PCIe cable "wasn’t spawned due to Thunderbolt, it was
more about the shift to thin notebooks and tablets that means you just can't
mechanically package things the same way we used to," said one source close
to the effort who asked not to be named.

"Thunderbolt was interesting, but it did not solve the problems we have the
way we want to have them solved," the source said.

Thunderbolt uses a router chip on either end of the connection to support
multiple protocols and daisy chaining of devices. Apple "is fine with the
extra cost of the router chips, but we don’t need [the multiprotocol support]
and a couple extra chips don't make business sense for us," the source said.

The use of four parallel channels and a thinner cable and connector are also
expected to give the PCIe approach a leg up over Thunderbolt in throughput
and ease of supporting thin systems.

Intel introduced Thunderbolt in February when Apple debuted MacBook computers
using it. It uses five wires to support two 10 Gbits/s bi-directional
channels on a common transport layer that can carry 4x PCIe Gen 2 or
DisplayPort traffic.

A handful of system makers said they support Thunderbolt including executives
in Canon's camera and video group. LaCie, Promise Technology and Western
Digital said they will support the interconnect in external drives. A handful
of other companies said they will provide support in mainly software

Other than Apple, only Sony has so far been reported to have plans to support
Thunderbolt. The PCI SIG's decision to create a competing technology suggests
mainstream PC makers on the PCI SIG board such as Dell and Hewlett-Packard do
not want to adopt Thunderbolt.

When Thunderbolt was announced, at least one top PC maker said privately the
company is moving ahead with USB 3.0 as a fast external interconnect. It is
less interested in Thunderbolt than in seeing Intel more aggressively support
USB 3.0, he said.

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