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Old January 23rd 05, 01:21 AM
Robert Hancock
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Paul wrote:
The additional bandwidth offered by PCI Express might be
the next argument someone would present. But the PCI
standard already has options for giving users more bandwidth,
(like 64bit/66MHz clock etc). And yet, it never seemed to
make sense, for anyone to offer those enhanced standards,
in the form of desktop chipsets. Server motherboards have
the slots, but not desktops.

The reason being it is too expensive. Increasing the clock rate or
adding more wires onto the bus makes the board design more difficult,
which makes it more expensive to design, plus making it more likely that
more layers will be needed in the PCB, etc.

The AGP slot is a point to point connection to begin
with. The Northbridge is on one end, and the AGP card
is on the other end. There is nothing to improve on there,
as far as the electrical connection.

One problem being, AGP has no provisions for more than one slot, making
such applications as SLI impossible or impractical.

The additional bandwidth of the PCI Express bus is a
waste, and if you check some of the review sites, they
demonstrate how much of the bandwidth is needed. For
the current generation of GPU (video card chips), PCI
Express isn't helping. And, as GPU chips are pretty
near the limits of their performance anyway, it remains
to be seen whether PCI Express bandwidth will ever be
saturated at the x16 level.

Bandwidth saturation isn't the only issue, there are other things such
as latency and guaranteed bandwidth allocation that PCI Express also

PCI Express means that a whole bunch of addin cards and
chips, will have to be redesigned. The cost of that
redesign will be passed on to the customers. So, don't
be surprised if a PCI Express LAN card or sound card
is a lot more expensive than the vanilla PCI one it
replaces. And the price of these cards will be higher
than it needs to be, even though the functionality of
the cards, to the end user, will be exactly the same
as the old PCI ones.

Sound cards aren't going to be a prime market for PCI Express cards for
a while, since they don't need the bandwidth. LAN cards likely will be,
since it's not possible to get full performance on a Gigabit Ethernet
card on a 32-bit PCI card, as well as SCSI and RAID cards.

I am all for superior technology replacing inferior
technology. The problem in this case, is so many years
have passed, that the inferior technologies we have been
using, have been tweaked to perform without problems. For
example, smaller geometry CMOS circuitry has made it
possible for virtually all Northbridge chips, to have
AGP 8X slots that work without a problem, whereas a
few years ago, there was a huge pile of duff boards
with bad AGP. If this superior technology had been
introduced years ago, when AGP sucked, I could
understand the need for the introduction of PCI Express.
The introduction at this point in time is unnecessary,
and is only intended to separate customers from their

The problems with some motherboards and AGP weren't due to lack of
technology, they were due to shoddy design (VIA being a big offender).
Intel's chipsets generally had no problems with any version of AGP.

They could easily have kept AGP and the current Northbridge
intact, and introduced PCI Express bridging in the
Southbridge. They could have offered a single x4 PCI Express
slot, for use with high bandwidth controller designs. That
would have caused virtually no additional cost to consumers,
and offered a slot with enhanced bandwidth, for use with SATA2
RAID or other exotic controllers. If the North-South bus
needed to be enhanced, to support such a change, the
change would be transparent to the end user.

What would have been the point of this? If you're not going to use the
faster bus for the most performance-demanding component - the video card
- what is the use?

A PCI Express serial interface runs at 2GHz. This is a
barrier to entry, for the "lesser" CMOS technologies. It
means the fab which is located 2 miles from me, cannot
make PCI Express parts. A lot more fabs could make
ordinary PCI chips, and as a result, this is why we can
find barrels of PCI Ethernet cards at the computer store
for $10 a piece.

Of course some manufacturers will have to retool, the same would have
been true when moving from ISA to PCI but few would say that wasn't

Robert Hancock Saskatoon, SK, Canada
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