On 7/3/06, Lowell Gilbert <[EMAIL PROTECTED]> wrote:
"Nikolas Britton" <[EMAIL PROTECTED]> writes:

> On 7/3/06, Lowell Gilbert <[EMAIL PROTECTED]> wrote:
>> "Nikolas Britton" <[EMAIL PROTECTED]> writes:
>> > What are the difference between the Intel PRO/1000 PT Server and
>> > Desktop Adapters?
>> >
>> > Intel PRO/1000 PT Server Adapter: $130 ~ 150
>> > Intel PRO/1000 PT Desktop Adapter: $40 ~ 60
>> >
>> > Both use the i82572EI chip and both appear to use the same PCB. Would
>> > I be correct in assuming it's a marketing scam to get 2.5 times the
>> > price for the same device?
>> Look at the specs; they use different controllers (from the same
>> family, so they may well work in the same PCB, but distinct in
>> capabilities).
> To clarify, I'm looking at Intel's PBs (product briefs) here:
> Look at the first line in the Features list on the first page, Both
> PBs list the same "Intel 82572EI Gigabit Controller".

Hmm.  Sorry, my notes seem to be wrong (or, given this market, quite
possibly just out of date).  I thought the "desktop" version was based
on something else (82751, I would have guessed).

The 82571EB is for dual port adapters.

>> They also have different bus interfaces -- which
>> could be a sustantial speed advantage for the server version under
>> high load.
> Again the PB clearly states both cards are PCI Express 1x... Just look
> at the photo in the PB... The cards are identical!

I still think there's a difference there, though; the "server" version
seems to be 4x.

You must be thinking of the Intel PRO/1000 PT Dual Port Server
Adapter... that's a PCIe 4x device.

"Each lane utilizes two low voltage differential (LVDS) signaling
pairs at 2.5 gigabaud. Transmit and receive are separate differential
pairs, for a total of 4 data wires per lane." [1]

"PCIe 1x is often quoted to support a data rate of 250 MB/s (238
MiB/s) in each direction, per lane. This figure is a calculation from
the physical signalling rate (2.5 Gbaud) divided by the encoding
overhead (10bits/byte.) This means a 16 lane (x16) PCIe card would
then be theoretically capable of 250 * 16 = 4 GB/s (3.7 GiB/s) in each
direction." [1]

To summarise, PCIe 1x is 2.5Gbps each way (dual simplex). After you
calculate in overhead (20%) you will have approximately 2Gbps, or
250MB/s, to work with. This is more then enough for a single gigabit
ethernet connection but not enough for two of them, PCIe 4x is 10Gbps
- 20% overhead (8Gbps) each way.

[1] http://en.wikipedia.org/wiki/PCI_Express

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