Feeds

Battle of the Buses? Not really

InfiniBand, HyperTransport, RapidIO, PCI-Express

  • alert
  • submit to reddit

Maximizing your infrastructure through virtualization

Server Briefing The bottom line: today's servers need more system bandwidth - a lot more bandwidth. Faster processors need to be pumped with instructions and data if they're to process information efficiently. Increasingly, that information comes from multiple sources within the box and outside of it. And the processed data has to be passed on to ever more users through permanent 24x7 connections.

In short, the old PCI bus has been pushed to its limit. Some applications have gone beyond it, necessitating alternative technologies to supply the bandwidth that PCI can't provide. Almost all PC graphics cards now require a dedicated bus, AGP. And in almost all high-end systems, chip-to-chip technologies like Intel's HubLink have ousted PCI from the role.

In the server world, the strategy of utilising multiple PCI buses has emerged, but at the cost of adding the extra host-to-PCI and PCI-to-PCI bridge chips, increasing power consumption, size and prices.

Clearly then PCI needs a successor, and there are already four main challengers for the role: InfiniBand, HyperTransport, RapidIO and PCI-Express. It's easy to view them as competitors, as fervent AMD and Intel supporters are keen to do, given each companies support for certain technologies, but while there's some cross-over, there's also plenty of opportunity for co-existence. And perhaps even interoperability, as witnessed by moves to align RapidIO and PCI-Express, for instance.

All the players certainly improve on PCI, offer many times greater bandwidth and far lower latencies. All seek to minimise power consumption and system real estate through lower pin counts. All transfer network-style packet-based data structures over point-to-point links. InfiniBand, HyperTransport and PCI-Express are serial architectures; RapidIO a parallel one (though a serialised version of the bus is in the works).

Not that PCI is entirely past it, having evolved into PCI-X with its system bus-level 133MHz frequency and 1.066GBps bandwidth. It's already being used in servers to hook up high-bandwidth fibre channel, SCSI and Gigabit Ethernet cards. The recently released preliminary 2.0 spec. takes PCI-X to 266MHz and 533MHz, to double and quadruple, respectively, the available bandwidth. That paves the way for 20Gbps InfiniBand 4x mode support, which is rapidly becoming the InfiniBand entry level - hence Intel's decision to get out of InfiniBand silicon development, having devoted its resources to 1x.

PCI-Express will offer sufficient bandwidth for a direct connection to 4x InfiniBand, but with hardware unlikely to appear before late 2003 or early 2004, PCI-X 2.0 should continue as an interim technology for now.

Unless, of course, HyperTransport proves a success. Like PCI-Express, it addresses the limitations of PCI and PCI-X, and with AMD committed to building it into Opteron server chips scheduled to ship early next year, there's a real opportunity to get in ahead of PCI-Express and provide high-bandwidth connections between InfiniBand fabrics and the CPU.

InfiniBand support is essential, since it's clearly the basis for data centres of the future - 3-4 million of them by 2005, according to InfiniBand chip maker Mellanox. InfiniBand is really about box-to-box communications, allowing servers and storage units to talk to each other directly across a mesh of switched peer-to-peer links.

That leaves HyperTransport and PCI-Express battling it out for the local bus. But it's hard not to see the real choice being not system logic but between the CPUs they connect. AMD customers will get HyperTransport; Intel customers PCI-Express. Both will hook up to InfiniBand and to legacy PCI hardware.

HyperTransport, with its very low latencies, also targets the embedded and networking markets, as does the Motorola and IBM-backed RapidIO. Again, choice of processor should govern choice of system logic - certainly both offer comparable performance and functionality. PowerPCs with RapidIO built in are expected to start shipping later this year, some of which are likely to make it into low-power blade servers. ®

The Power of One eBook: Top reasons to choose HP BladeSystem

More from The Register

next story
Sysadmin Day 2014: Quick, there's still time to get the beers in
He walked over the broken glass, killed the thugs... and er... reconnected the cables*
Auntie remains MYSTIFIED by that weekend BBC iPlayer and website outage
Still doing 'forensics' on the caching layer – Beeb digi wonk
SHOCK and AWS: The fall of Amazon's deflationary cloud
Just as Jeff Bezos did to books and CDs, Amazon's rivals are now doing to it
BlackBerry: Toss the server, mate... BES is in the CLOUD now
BlackBerry Enterprise Services takes aim at SMEs - but there's a catch
The triumph of VVOL: Everyone's jumping into bed with VMware
'Bandwagon'? Yes, we're on it and so what, say big dogs
Carbon tax repeal won't see data centre operators cut prices
Rackspace says electricity isn't a major cost, Equinix promises 'no levy'
Disaster Recovery upstart joins DR 'as a service' gang
Quorum joins the aaS crowd with DRaaS offering
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Securing Web Applications Made Simple and Scalable
Learn how automated security testing can provide a simple and scalable way to protect your web applications.