> Pete Theisen wrote:
> So much for the backward compatibility that we grew up with back in the
> bad old 8088 8086 286 386 486 P 1 2 3 days. I guess not enough people
> were tossing out their old stuff fast enough for the importers to become
> billionaires rather than mere chump change millionaires.
It is not that at all. Your confusion on the subject was the intended goal
by the marketers of PCI Express to beat the PCI-X bus.
The follow up to PCI was PCI-X, and you could indeed install a PCI card in a
PCI-X slot. You usually only saw PCI-X in servers and high-end
workstations. This was because the only cards that would commonly use the
added bandwidth of PCI-X tended to be expensive RAID controllers. The
connectors are much larger, take up more space and cost more. So it was a
chicken-vs.-egg situation. If there are no PCI-X boards, it was hard to
justify the added cost. If nobody has a PCI-X slot, there won't be many
boards. So PCI-X was being adopted very slowly outside of the high
performance workstation / server market.
Meanwhile, another group was working on a completely different bus. It
started off as a serial bus, with a small inexpensive connector (perfect for
PCs). But then they gave it the ability to have multiple lanes of the serial
bus, so you could simply increase the number of lanes to achieve higher
bandwidth. So you have single lane cards with small (inexpensive)
connectors, and 4, 8 and 16 lane connectors where you need more performance.
This was all a very good thing.
Then the marketing guys got involved. Rather than create a completely new
name for the new bus, they expanded an old name and called it - PCI-Express.
This sounded like it was the "new and improved" PCI rather than a completely
new bus. Well, it worked - you see PCI-Express (abbreviated PCI-e)
everywhere. But it does cause a lot of confusion, especially considering
that you see the term "PCI-X" and think that means PCI-eXpress.
It would be tough to beat out the PCI card, so they aimed at the AGP slot.
AGP has nothing to do with PCI, and is only there as a dedicated high
bandwidth slot for graphics cards. So they produced 8-lane cards, and later
16-lane cards with much better bandwidth than AGP and won over that market.
The pitch was to use PCI-e for graphics and over time add slots for
single-lane PCI-e on the motherboard. At some point, you will have a
motherboard with nothing but PCI-e slots.
So the marketers made a mess of things for users and won the marketing war.
But the engineers did good - we have a new standard that works well and cuts
cost, yet has better performance. Yes, you can put a single-lane PCI-e card
in any PCI-e slot as long as it has the same or greater number of lanes as
the card. In fact, I needed a graphics card for a HP server that had a
8-lane PCI-e slot, but the cards where either 1-land or 16-lane. I used
Dremel to cut off the last 8 lanes of the graphics card and it worked fine.
How's that for backward compatibility?
Ken Elliott
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