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Getting Gigabit to desktops

Apr 07, 20035 mins

Standard, proprietary technologies on the way to speed PC buses.

Dramatic price drops on copper Gigabit Ethernet network interface cards and switch ports have caused many network professionals to take notice. But because many PCI-based desktop machines were not built for Gigabit-speed LANs, those users serious about migrating to high-speed PCs might have to upgrade more than NICs and wiring closet switches, some say.

“There are many efforts to get Gigabit Ethernet into the client area, and it will probably soon be a check-box item for enterprise IT staffs,” says Tony Pierce, chairman of the PCI Special Interest Group (PCI-SIG), a standards development group responsible for the PCI technology design.

Part of the attraction of Gigabit to desktops is the proliferation of inexpensive Gigabit NICs, with many available for less than $100. Switch vendors also are pushing copper-Gigabit desktop links, as Cisco last week released high-density 10/100/1000M bit/sec switch modules for its Catalyst 6500 switch, aimed at large wiring closet deployments. PC vendors such as Apple, Dell and HP also offer 10/100/1000M bit/sec ports integrated into their desktops.

For users thinking of slapping in 10/100/ 1000Base-T NICs on older desktops, Pierce warns “you will get better performance on those systems, but not at the level that you’d expect, and for the added expense you will pay for upgrading to Gigabit. A lot of it depends on system configuration.”

The issues lie with the PCI shared bus architecture, which has a total bandwidth of 133M byte/sec between peripheral cards and the processor and memory.

“The laws of physics tell you that you’re not going to get full-duplex Gigabit Ethernet throughput,” on older PCI systems, Pierce adds.

He says newer bus architecture technologies – such as PCI-X and PCI Express – are starting to catch on in server connections and will trickle down to PCs.

PCI has long been the standard bus interface for connecting devices such as NICs, RAID controllers, modems and other peripheral cards to PCs and servers. PCI-X 1.0 was introduced in 2000 as an extension of PC, increasing bus speed to 133 MHz. PCI-X 2.0 was introduced soon after PCI-X, offering higher bus speeds, from 266 MHz to 533 MHz. Last year, the PCI-X 1066 specification – a 1066 MHz bus with 8G byte/ sec of bandwidth – was launched. PCI-X 1.0 and 2.0 are used mostly in servers and some desktops.

Ultimately, the emerging PCI Express will be the standard bus architecture of choice for desktops and servers, Pierce says. That architecture promises up to 16G byte/sec, or 128G bit/sec, with a fully switched architecture. The advantage is similar advantages of switched Ethernet over shared hubs.

The here and now of PCI

For now, PCI-X 1.0 is used more widely on servers and some newer PCs, but the technology is not as widespread as standard PCI, Pierce says. And because mass adoption of the newer PCI variants probably won’t happen until next year, some vendors have created proprietary methods for making PCs and servers Gigabit-ready.

Intel recently released its Communications Streaming Architecture, which is an I/O technology that bypasses 32-bit, 33 MHz PCI bus systems and allows full duplex Gigabit Ethernet support for Intel NICs.

“With PCI and Gigabit Ethernet NICs, you have a very high-speed connection that’s forced to share bandwidth with other slots on the bus,” says Tim Helms, vice president of Intel’s communications group and general manager for its platform networking group. “We’ve removed the PCI bottleneck by offloading the LAN traffic from the PCI bus, to give it direct access to system resources.”

Helms says the new technology lets PCI-based systems push up to 1.7G bit/sec of bandwidth between the NIC and system memory and processor, up from about 928M bit/sec, which was the previous top performance on an optimally configured Intel PC or server.

“There are some technology that help improve Gigabit Ethernet performance on a PCI bus, but they are proprietary,” PCI-SIG’s Pierce says. “Some of these proprietary efforts were created due to the lack of a high-speed I/O standard that is widely available.”

While there will be users with immediate needs for full-Gigabit performance on PCI systems, ultimately standards support for a faster I/O technology will be more important to companies, Pierce says. By the time widespread demand for Gigabit desktops occurs, which he expects over the next few years, standards such as PCI-X 2.0, PCI-X 1066 and PCI Express will be available from equipment makers.

“In a few years, you will probably be looking at PCI-X or PCI Express as a replacement for most desktop systems,” he adds.

Subgig good enough for some

While technology options vary and new standards are under development, users who have installed Gigabit desktop connections today say the performance is adequate.

Aperio Technologies, a San Diego company that develops high-resolution scanning technology for microscope slides, uses Gigabit Ethernet NICs in its PCI-based desktops for moving large image files around its network.

“It’s a little slower than full Gigabit, like you would expect,” Ole Eichorn, CTO at Aperio.

“It still blows Fast Ethernet away,” he says, adding that he sees about 500M to 800M bit/sec data transfer rates between some machines. “When you’re moving a 2 gigabyte file from a PC to a server, [Gigabit Ethernet] is a nice thing to have.”

At Case Western Reserve University in Cleveland, the new facility for the business school was built with 10/100/1000M bit/sec ports to every office, classroom seat and common area in the building. Many students use school-issued Dell laptops with 10/100/1000M bit/sec cards, and faculty members use a mix of PCs and Macs with Gigabit built in.

“We’re not getting full Gigabit throughput, but we’re seeing about 80% to 85%, which is pretty good,” says Lev Gonick, CIO and vice president of IS.

Gonick says students use the Gigabit connections mainly to access the school’s large library of multimedia materials hosted on servers in its data center.