PCI Express SIG reveals future specifications

THE PCI-SIG WAS OUT in force at IDF touting their upcoming specs. By now you probably know about PCI-Express, or more technically PCI Express 1.0a. If you don't, go read about it, it is a huge change from PCI, and you will be using it in the near future. A very brief history is that it is a software compatible PCI replacement, but it goes much faster. A single channel runs at a 2.5GHz signaling rate at .8v. You can aggregate multiple channels in a single connector in bunches of 2, 4, 8, 12, 16 and 32, giving you a total bandwidth of 16GBps.

The first of the new stuff is PCIe 1.1. This is not a huge change, in fact they really don't add anything new, just a cleanup and preparation for the future. The first thing they did in this backwards compatible spec was to loosen up the timings a bit. The lessons learned with 1.0 told them where they had room to spare, and it was put to good use. Additionally, they rebudgeted the allowable jitter to clean things up a little bit more.

All of the changes they made are backwards compatible, pretty much a requirement. They also made room for four new specs, Server IO Modules and a high end graphics connector are the near term ones. Further out, about half way through the process, is a wireless form factor and a cable spec.

The Server IO Module is a neat idea. It is a hot plug module, not a card. If you have ever seen a hot plug SCSI drive, you get the idea, it is an enclosed 'thing' that can be put into and pulled out of box at will or whim. It will allow for things like replacement of drive cages, not just drives. Servers have needed this for a while.

The next one is the High End Graphics spec. It is not a connector that you plug cards into like the 16x slots, but a power spec. If you need more bandwidth, you could just go from 16x to 32x, it is already defined. This spec allows for the extra 2x3 power cable that like Clint Eastwood hasn't a name yet. They turned down my suggestion of Mortimer. A pity, it had a rung and a ring to it. The current version, not named Mortimer either, allows for 75w to be pumped through a 16x connector, less for lower amounts of lanes.

The new cable frees vendors from having to pull in a molex connector off an IDE device, and step it down to the correct voltage on the card. Instead, you can deliver up to 75w more through the cable at a more appropriate voltage. If the 150w total isn't enough for you, there are solutions up to 200w on the road map.

All of these specs are currently for the ATX form factor and in the near future, there will be a similar spec for BTX. Both of you out there who ran out and bought BTX systems, sorry, no 200 watts industry standard graphics cards for you.

Farther out on the horizon is the wireless spec. No, this is most definitely not a spec to transmit PCI Express signals over a wireless link, it is just a badly named spec. It actually covers a way to hook up a slim wireless transmitter that will be located a bit away from PCIe slots. The cards have a physical form factor with a much lower Z or depth, and can be cabled out to remote parts of the system. They will be ideal for 802.11 cards placed on the back of a laptop screen. Wireless is about wireless cards, not wireless signals, get it now? Look for it in the first half of 2005.

A bit further out is the PCIe cable spec. It allows you to put a device on the end of a cord. This one is still a bit contentious, mainly because it has such a high demand. Some vendors really want a low voltage three metre cable, others simply must have a 10 metre cable that transmits lots of power.

PCI-SIG meetings discussing this must be tons of fun to watch, with many creative names for people's mothers flying back and forth. Because of this, the spec is due a bit later than the wireless one, about mid 2005, give or take a bit. Once it comes though, you will probably see a tonne avoirdupois of neat data centre tricks popping up.

So, the PCI-SIG people have been busy with three new specs due in the short term, and two others shortly after that. Further out, we have PCIe 2.0 which does things like raise the fundamental 2.5GHz signaling rate. This spec is still nascent, so don't hold off buying a new system just for it. It just shows that PCIe is alive and well, and there is a road map for the future.