[SI-LIST] Re: PCI at 66 Mhz
- From: Michael Nudelman <mnudelman@xxxxxxxxxxx>
- To: "'p2rich@xxxxxxxxxxxxx'" <p2rich@xxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Tue, 4 Sep 2001 12:49:55 -0400
What I never understood (though I successfully designed a PCI-bus-equipped
board in the past, 33MHz, which was easy - with this speed you do have lots
of slack) is the idea behind the whole PCI mess.
Reading the MindShare Book (probably the best book for a PCI designer), the
main Idea I understood - it is a "green" bus, hence the whimpy drivers, long
slew rates, possible stepping and ... uhhhh... reflective switching.
Now, if you want the maximum speed (and the 66MHz is fast! Everything above
30MHz is fast enough to require some attention of the designing engineer)
you want minimum setup time.
The reflective switching adds the reflective run to the setup timing,
possibly doubling it in the worst case. This way you have very short bus
with few (if any!) loads allowed.
Now, if the "green" architecture is behind all this, tell me, how much
energy on the whole computer scale (percent-wise) do you really save on the
PCI data transfer? And is it worth it to complicate the design?
After all, if the CPU and memory use 133, 266, 400MHz transfer speeds, which
are also incindent-type, and by no means could be considered "green", why
discriminate against peripherals, which are also becoming inreasingly fast
and require faster and faster transfer rates.
If 6 years ago a rate of 3-6MBs for a graphic card was considered a "greased
lightening" (exerpted from MATROX ad in a magazine), today it is a "dead
snail". A harddisk became few times faster than memory used to be.
Why keep using PCI?
Mike N.
-----Original Message-----
From: Rich Peyton [mailto:p2rich@xxxxxxxxxxxxx]
Sent: Tuesday, September 04, 2001 11:44 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: PCI at 66 Mhz
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I ran across this today, I thought it would be of interest to whomever
started the above subject.
"Electrical -design considerations for PCI-X & 66MHz PCI Cards" in EDN
Magazine.
http://www.e-insite.net/ednmag/index.asp?layout=article&articleid=CA152874&p
ubdate=8/30/01
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