weird question: what would be the max transfer rate (roughly) of a 64bit
PCI-X gbe card, that was installed on an older UDMA33 motherboard (with
pentiumIII) with 32bit PCI slots and ATA100 hard drive...? how would
this compare to more modern UDMA100 motherboard (still only 32bit
PCI)...? and then what is the actuall max transfer rate if that gbe card
was in a PCI-X slot...? cheers.

"Paul Gunson" <paulg@spammenot.com> wrote in message
news:bufno0$h1p$1@lust.ihug.co.nz...
Well, there are two things to clarify here. First, whether the motherboard
supports UDMA33 or 100, has no bearing on the PCI spec of that motherboard;
they are just separate features. Second, the PCI-X card will operate like a
regular PCI card if plugged into a regular PCI slot; so none of its 64-bit
features is enabled.

So the transfer rates of various PCI buses:
32-bit, 33Mhz PCI: 32 * 33 / 8 = 133 MB/s
64-bit, 33Mhz PCI: 64 * 33 / 8 = 266 MB/s
64-bit, 66Mhz PCI: 64 * 66 / 8 = 533 MB/s


So a Gigabit Ethernet card by definition has a maximum transferal rate of
125 MB/s (1000 Mb/s / 8). So the GBE card will pretty much saturate the
whole 32-bit 33Mhz PCI bus, if it goes at its maximum speed.

Yousuf Khan

"Paul Gunson" <paulg@spammenot.com> wrote in message
news:bufno0$h1p$1@lust.ihug.co.nz...
32-bit PCI peaks out 60 mb/s (older chipsets, most Via chipsets) to 90 mb/s
(modern intel chipsets). Other limiting factors: Ability to process a large
number of TCP/IP packets per second (you need a 2 GHz class machine and a
"server" class GbE card to saturate a GbE link) and actually getting data
from the disk at that speed.

With an older P3 and UDMA/33 don't bother. You'd need to add an UDMA/100 PCI
controller card, then however the data gets transferred over the PCI bus
twice and you loose again.

If you decide to upgrade, get an intel mainboard with "CSA" GbE.

Martin

Martin Kuhne wrote:


thanks for the info - i already have a 3com PCI-X GbE card (3C996B-T).
some software i have requires a licence locked to a NIC so i bought a
really awesome NIC that would last a while (long story).

anyway my old dual PIII with UDMA33 is horrendously outdated, so i will
keep the NIC and upgrade in about 3 weeks. am considering AthlonXP 2800+
(2GHz), or maybe even MP2800+, 'cause the MPX boards have the PCI-X
slots. i'm guessing that the bandwidth on an older MPX board is still
greater than that of a newer XP board (with an nForce chipset), that
doesn't have PCI-X....?

Opteron would be nice but insanely expenive.

"Paul Gunson" <paulg@spammenot.com> wrote in message
news:bun1mj$l4j$1@lust.ihug.co.nz...

MPX certainly sounds interesting, on paper it has 4x the PCI bandwidth and
two independent PCI buses! The memory interface is not as good as on Kt600
or nforce 2 but it should not be too bad.

I have not read of any reviews or benchmarks where somebody would have
really pushed the 66 MHz/64bit PCI bus on the MPX so you have to take their
word for it ;-)

Martin