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- Newsgroups: comp.arch
- Path: sparky!uunet!cs.utexas.edu!wotan.compaq.com!twisto.eng.hou.compaq.com!croatia.eng.hou.compaq.com!simonich
- From: simonich@croatia.eng.hou.compaq.com (Chris Simonich)
- Subject: Re: COMPAQ PROPOSED SCALABLE I/O ARCHITECTURE
- Message-ID: <1992Dec16.160054.2486@twisto.eng.hou.compaq.com>
- Sender: news@twisto.eng.hou.compaq.com (Netnews Account)
- Organization: Compaq Computer Corp.
- References: <1992Dec15.171554.2781@twisto.eng.hou.compaq.com> <1992Dec15.194637.10009@eng.umd.edu> <1992Dec15.205639.25591@super.org>
- Date: Wed, 16 Dec 1992 16:00:54 GMT
- Lines: 39
-
- In article <1992Dec15.205639.25591@super.org> rminnich@super.org (Ronald G Minnich) writes:
- >
- >Actually, seems to me they could look at SCI. Except they want low cost.
- >But if the CMOS chips for SCI pan out, maybe they will meet the cost
- >range.
-
- We have received this response from several people. We
- disagree. For one SCI had a physical topology (a ring) that
- is not suitable for expansion I/O. Yes, we know you can run
- the ring to and from the same board and create a topology
- that looks like the Anet (Compaq Proposal) topology but then
- you begin to loose much of the cost advantages. We took a
- long look at SCI before we created our proposal. We ran
- into lots of problems trying to allow different speed rings
- to work together and the biggest problem was that we didn't
- like having to have bi-polar transceivers. When we started
- to recast the thing for CMOS implementation we ran into
- protocol inefficiencies and, well, it just didn't seem to
- work out the way we need it to. The major thing turned out
- to be that SCI and the Compaq proposal (we call it Anet
- around here) were trying to solve different problems with
- cost, not bandwidth, being the major one. The fact that the
- 'C' in SCI stands for coherent I think brings out one of the
- differences in approach. We needed an I/O interface and
- coherency in the I/O subsystem was something that we were
- trying to eliminate. The address bandwidth required to
- maintain coherency in the I/O subsystem is prohibitive.
-
- Don't get me wrong, we think that from a technical point of
- view SCI is neat. It just seems to be intended for a
- different part of the system architecture. We would welcome
- any comments you have to the contrary. When/if you respond,
- tell us how we can make an SCI, I/O subsystem as cheap as an
- Anet, I/O subsystem.
- --
- ======================================================
- Christopher Simonich simonich@twisto.compaq.com
- Compaq Computer Corp. [713] 374-1898
- ======================================================
-