From: michael@Canada.lsil.com (Michael Smith)
Subject: Re: Intel's new PCI archictecture
Reply-To: michael@Canada.lsil.com
Organization: LSI Logic Corporation of Canada, Inc.
Date: Wed, 23 Dec 1992 13:10:49 GMT

In article Kx@utdallas.edu, goyal@utdallas.edu (MOHIT K GOYAL) writes:
>Well, with the "is EISA or VL-Bus better" pretty much becoming a FAQ, I will
>add a new twist.
>
>I just read that Intel is going licence its new PCI architecture to hardware
>manufactures for *free*!
>
>I know that a few, very few, are going to start coming out in January, but
>I'm wondering how much this might help.
>
>I'm under the impression that Intel is the only company who can make the
>PCI chipset.  Anyone know when a clone might be out?  (Isn't it true that
>only in the 2nd half of 1992 did a "cheap" EISA clone come out?)
>
>All I know about PCI is that it will be 32-bits wide and run at 33mhz.
>
>I don't know how it is layed out, if it is backward compatible, if it is
>simply "EISA at 33mhz" (in terms of features).
>
>EISA at 33mhz will be nice.
>
>I wonder how it will perform in 50mhz 486's, and 66 & 100mhz 586's.
>


PCI is Intel's new "Peripheral Component Interconnect" bus.  The complete bus spec
is available from Intel for less than $100, though to become a SIG member, this
is considerably more.  So yes, $100 is essentially free, the few thousand (if I 
recall correctly) for SIG membership is also minor if you're a manufacturer.  There
aren't any licensing deals, or anything of that sort.  

Intel has a "Saturn" chipset that is 486 based, that supports the PCI bus.  There
are many PCI devices that are currently being worked on, including other chipsets.
The Saturn chipset is the first, but others will undoubtedly be out in '93.
EISA chipsets have been out for quite some time, but silly engineers keep insisting
on making them 2 chips, or up to 3 or 4 chips instead of a single chip.  This drives
up the cost considerably, and thus their lack of popularity.

No, PCI is not EISA at 33MHz, it is a completely different bus.  It is also
expandable to 64 bits wide, although it is not known at this time how many
systems (chips) will support this wider format.

As for performance with 50MHz 486, and the various Pentium products, the CPU speed
here is not really an issue.  PCI is primarily meant to be a "Peripheral"
bus, i.e. an expansion card I/O bus.  I/O is inherently slow compared to the CPU.
Although there will be more traffic on this bus with a faster CPU, this bus will
see a great deal less traffic than the CPU's local bus.  Any bursts to this bus
can easily be smoothed out with some simple buffering.

Shouldn't these sort of questions really be on comp.arch?

---
     Michael Smith - Chipset Design Engineer

Phone: (416) 620-7400         michael@canada.lsil.com
Fax:   (416) 694-5005

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