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From: mdeale@cosmos.acs.calpoly.edu (Myron Deale)
Newsgroups: comp.arch
Subject: IPI-2 vs. SCSI
Message-ID: <13698@polyslo.CalPoly.EDU>
Date: 20 Aug 89 12:51:40 GMT
Sender: news@polyslo.CalPoly.EDU
Reply-To: mdeale@cosmos.acs.calpoly.edu (Myron Deale)
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Organization: ACS, Cal Poly, San Luis
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Hello,

   there was an article in a major electronics journal lately that
suggests "the industry is moving to IPI."  IPI stands for Intelligent
Peripheral Interface, of course. I guess Imprimis has announced an
8in. drive w/ dual read channels capable of 6 MB/s, sustained or
peak I'm not sure, and a native IPI-2 interface. Not bad :)

   But why go with an under-developed interface such as IPI-2 ?
SCSI has a lot of software supporting it which implies it is reasonably
well understood; you can get cheap SCSI protocol IC's that'll go
5 MB/s; and the prices are lessening as momentum picks up.

   Both IPI and SCSI have upgrades in the planning process. SCSI
plans to go 40 MB/s (through "wide" and "fast") and IPI is projected
to go 50 MB/s with a max cable length of 50m when ECL drivers are
used. Someday IPI may go to fiber optic cabling, but that may
compete with FDDI or SONET. In addtion, there's one company that
markets protocol chips for IPI; they sell a set of 4-5 chips w/
an average liscensing fee above $50,000 ... and don't forget the
cost of the chips. Sounds like a lot of samolians.

   Maybe I'm missing some key facts, but is there any advantage
to design with/for IPI ?  If you want high-end communication speed,
like between a super' and it's "front-end I/O" handler you might
plan for Hyperchannel or FDDI. If you want to hook up blinding
disk bandwidth directly, then you might want a parallel disk array.
Or if you want reasonable speed with mainstream products, then
you might design with SCSI (and upgrades) and allow more controllers
to be added by the consumer.

   Summary: I just don't see any significant improvement for IPI
over SCSI. Perhaps what's needed is a RISC version of SCSI :^)


-Myron
// mdeale@cosmos.acs.calpoly.edu
PS. What is CDC thinking, selling off Imprimis?