New hardware doesn’t have to cause problems

Fred langa By Fred Langa

Usually a major hardware change causes endless software hassles. It doesn’t have to be this way.

If your current PC doesn’t have "PCI Express" technology, your next one most likely will. Here’s the scoop on PCI Expressand what it means for Windows users.

Using Windows with PCI Express hardware

Reader Bob Spaith encountered a problem that will become more and more common as new hardware technology moves into our Windows PCs:
  • "I’m wondering what the main differences are between PCI and PCI Express. I’m using a motherboard that only has PCI slots, and I am using an Adaptec SCSI controller card that is PCI Express. I was told that Windows will work with the PCI Express card in a PCI slot (and it does), but part of the card does not have a socket to plug into, so it is not connected to anything.

    "I would like to know what is lost by using a card like this? Speed? True compatibility? I don’t really understand how the card can operate correctly when part of it is not plugged into anything."

Hmmm. Something’s not right there, Bob, so let’s take a moment to sort out some technologies with confusingly similar names.

First, for clarity: PCI and PCI Express are electrical "buses." A bus is a series of connections that your PC’s components and subsystems use to communicate with each other.

Most PCs today are built around the original PCI (Peripheral Component Interconnect) parallel architecture introduced back in the early 1990s. PCI was a replacement for the even older first-generation ISA (Industry Standard Architecture) and EISA (Extended ISA) architectures. These last two bus types have all but vanished from current PC motherboard designs.

Toward the end of the 90s, PCI technology spawned two offshoots. In 1997, Intel introduced AGP (Accelerated Graphics Port), which is a variant of PCI architecture designed specifically for higher-speed graphics cards. In 1999, a consortium of hardware vendors launched PCI-X. This is not PCI Express, but rather "PCI eXtended," which is another variant on classic PCI’s parallel-connection technology designed to increase throughput speed.

A 32-bit PCI-X card can fit into a standard 32-bit PCI slot without problems (although it may have extra connectors "hanging over" the edge of the slot). The PCI-X card will run just fine in a PCI socket, albeit at the slower speed of standard PCI.

Although AGP is also a close variant of classic PCI technology, AGP uses a special slot or socket that won’t accept standard PCI cards. Most PCs sold today have several standard PCI and one AGP slot. In fact, the PCI/AGP combination is all but ubiquitous. PCI-X is still around, but much less common.

PCI Express is an entirely different animal. Originally called "Third Generation I/O" (3GIO) and introduced in 2002, PCI Express is a high-speed serial bus that can run at up to 10 GHz, as opposed to the approximate 1 GHz practical limit for conventional PCI’s parallel architecture.

PCI Express cards usually have special slots or sockets. Normally, you can’t plug a PCI Express card into any standard PCI slot — even if it fits, PCI and PCI Express use fundamentally different architectures (parallel versus serial), and so they’re unlikely to work unless the card has some ability to switch types, which depends on what kind of socket it’s plugged into.

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All Windows Secrets articles posted on 2007-02-15:

Fred Langa

About Fred Langa

Fred Langa is senior editor. His LangaList Newsletter merged with Windows Secrets on Nov. 16, 2006. Prior to that, Fred was editor of Byte Magazine (1987 to 1991) and editorial director of CMP Media (1991 to 1996), overseeing Windows Magazine and others.