As BYTE is now a subscription service I thought some people might enjoy reading some extracts.

PCI Express: The Future of the PCI Bus

WinHEC isn't just about Windows. At what may have been the first WinHEC I ever attended, one of the speakers asked the 4500 or so engineers present "How many of you would like to take the ISA bus out in the parking lot and shoot it?" He got rousing cheers.

Since then the ISA bus has indeed gone away, and the PCI bus that replaced it is on the way out.

As computers have gotten faster, bus speeds have become more of a bottleneck. CPUtomemory bandwidth has increased from 800 MB/s with PC100 memory four years ago, to the 6.4 GB/s of the Intel Canterwood (875P) chipset with dualchannel DDR400 memory today. Incidentally, while I won't have a lot of room to talk about it this month, I continue to marvel at the performance of my Canterwood systems (see the April column). Everything just works, smoothly and efficiently, and they are FAST.

While clock speeds have gone to 3 GHz, CPU bus speeds haven't kept up with clock speeds, but they have increased more quickly than peripheral bus speeds: the PCI bus. Yes, highend PCs have begun to ship with 64bit buses, and the very latest 64bit slots also run at 66 MHz. That's four times the throughput of the usual 32bit, 33 MHz slots we're all familiar with. The latest slots (mostly in servers today), PCIX, double that again. Still, that's only 8 times faster than last year. By the time Longhorn ships, midmarket PCs will be moving enough data around that you'll actually feel the pinch.

In anticipation of this bottleneck, at last year's WinHEC, the PCI SIG announced PCI Express, a new, serial bus designed to supplant both PCI and PCIX. Despite the unfortunately similar name to PCIX, PCI Express (or just "Express Bus") is a completely different hardware standard: Where all previous PCI buses were completely parallel, all Express connections are serial, and pointtopoint. Fortunately, the associated software for Express Bus is a complete superset of PCI; for developer drivers and the operating system, cards will Just Work. (More on that in a moment.)

The smallest Express channel is one bit wide, one serial channel to a connector. To get more speed, a single Express expansion slot can have one, two, four, up to sixteen channels, each one bit wide. Narrower cards (say, a Gigabit Ethernet card, with a connector supporting a single channel) will plug into wider Express slots (say, a slot with four channels). As cards need more speed, manufacturers will simply implement more channels. You'll just plug the card into any available slot, so long as it fits. Peter Glaskowsky thinks it's a mistake ever to include a single Express channel slot on a motherboard: The minimum size slot should be 4 channels.

It is also worth noting that PCI Express will also make it to next generation laptops under the guise of the NewCard specification, as it is currently called. NewCard based devices will have either a 2bit or 4bit wide PCI Express interfaces. NewCard will not support graphics cards like in desktop PCI Express. Those will still remain in the domain of the laptop motherboard. For more on this see this article.

Flash forward to 2003. This year's WinHEC has an entire threeday track on implementing the Express Bus. These tracks were long, involved, full of examples and too technical for anyone not directly involved in implementing the technology. Microsoft clearly thinks Express is real, important, and that they need to shape the way peripheral card companies implement their expansion cards. This level of commitment is particularly important for graphics cards, video capture cards, and very highspeed Ethernet cards: Such cards will want to reserve a known size of channel to the rest of the PC, using isochronous communication.

By the time Longhorn ships, PCs will ship with Express Bus—first as an addition to regular PCI slots, then as a replacement. With luck, cards will have stable and complete drivers, too. Microsoft has been working hard to get driver development under control with stability as a primary goal, and we can all applaud those efforts. WinHEC is one of the primary ways they do that.

Serial ATA and connectors

Anyone who has built or rebuilt a PC in the last ten years (that should be just about all my readers) has grumbled and griped about the wide, thin ribbon cables you use to connect hard drives and optical drives to the motherboard. Parallel ATA cables are a pain. They are never the right length, they get in the way, you can unknowingly knock them slightly loose, and they impede airflow. None of that should come as news.

In just the same way as the parallel PCI bus is migrating toward the serial PCI Express bus, Parallel ATA is being replaced by Serial ATA (SATA). The current version of SATA is embedded on the Intel Canterwood (875) motherboards, and nearly every other motherboard company offers it. SATA hard drives are still somewhat thin on the ground; Maxtor was widely expected to be first to ship in volume, but they haven't made the cutover, yet. Seagate is already shipping drives, and the other companies are waking up.

Maxtor is shipping 10,000 rpm 36.7 GB Enterprise class SATA hard drives. Seagate has an 80 GB, a 120 GB and now a 160 GB SATA drive on the market; I have two of those in my latest Canterwood machine. Maxtor's 160 GB SATA hard drive has been announced but no one has it in stock yet. I expect to get a pair of those pretty soon.

The SATA spec is now mature enough to be taken seriously by the entire PC developer community; I would be surprised if it were not so, since the interface is completely transparent to the OS, and the price is nearly identical to PATA. About the only complaint I've heard about SATA is that there's no standard for external connectors; it's designed for exactly one cable, running from the drive directly to the controller board.

I'm told SATA is also making real headway in the storage networking universe, which is finally tired of paying the 2X or 3X price difference for SCSI vs. ATA drives. Here at WinHEC, the exhibits floor has at least five demos of SATA adapter cards, either for chips to be embedded on motherboards or as RAID controllers. That 8drive RAID array on display can hold 2 Terabytes, with 250 GByte drives. Companies like 3Ware now ship SATA controllers that support 12 drives, or 3 TBytes; is it any wonder that we need a faster PCI?

Next on the horizon is the SATA 2.0 spec, which will greatly increase the connect speed over the current 150 Mbytes/second. In other welcome news, we buttonholed the representative from the SATA Special Interest Group, who swore a mighty oath that an external connector spec would be hammered out, before SATA 2.0 is done—and hubs are coming, so you can connect to a box of drives.

You'll recall that my newest system at Chaos Manor has a dual disk Serial ATA RAID built onto the Intel Canterwood chipset motherboard. It works fine. You will need two identical hard drives to implement it. I'm pretty sure SATA is the wave of the future. It will replace parallel ATA, and while it won't replace SCSI it will marginalize it.

On The Road

I also use WinHEC as a test run for the latest road warrior gear, both on the trip and at the conference itself. Microsoft always sets up a network with both wireless and high speed Ethernet connections to the Internet as well as to the show data base. The wireless is especially interesting: One year I was able to send to my web site in real time pictures of Bill Gates making his keynote speech. I used the Microsoft local wireless LAN for that. This year the wireless net didn't reach into the conference area, and there were other problems we'll get to later. So it goes.

This year I am carrying both Lisabetta (the Compaq/HP Tablet PC) and my old reliable Royal Armadillo (the COMPAQ Armada 550) but so far the 550 has only been a backup, and the Tablet has done all the work. There have been a few problems, but in general it has worked out well. The Tablet has builtin wireless, and that works too, although it doesn't seem to work as well as the wireless built into Peter Glaskowsky's Titanium Apple Power Book G4 15 Inch Model. His has a "SuperDrive," a slotloading DVD writer. The Power Book is also easier to get connected to the net: As Peter says, with Apple systems, everything is either very simple, or impossible; and with the latest Apple OSX, a great many more things have become possible.

Eventually, though, I was able to get connected, both with wireless and with the fast Ethernet connections available in the press room.

From f* Thanks Steve.