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From: aland@infmx.UUCP (Colonel Panic)
Newsgroups: comp.unix.i386
Subject: Re: SVR3.2.2 on an EISA machine?
Summary: memory CAN be > 16MB with AT&T SVR3.2.2
Message-ID: <4424@infmx.UUCP>
Date: 5 Jun 90 22:23:22 GMT
References: <1990May31.185133.21581@maverick.ksu.ksu.edu> <1990May31.231831.19959@ico.isc.com>
Reply-To: aland@infmx.UUCP (alan denney)
Organization: INFORMIX Professional Services ("Peace thru Normalization")
Lines: 27

In article <1990May31.231831.19959@ico.isc.com> rcd@ico.isc.com (Dick Dunn) writes:
>...
>What's the real picture?  If you get an EISA box now, and you're careful
>to put in devices that also operate as ISA devices, and you don't put in
>too much memory (since ISA is limited to 24 bits == 16 Mb), you're OK with
>the various V.3.2 systems just as they stand.  There's an obvious speed

Uh, almost.  The way I read this is that you are saying that you can't
have more than 16 MB on an ISA machine, which is untrue.  The current
AT&T 6386 line, for example, supports 40 MB.  I'm running a bunch of
them with 24 MB right now.  (Since the memory boards are so expensive
and can hold 16MB each, and going from 16 to 24MB costs just the extra
SIMMs, it's cost-effective).

The only real gotcha is DMA.  AT&T SVR3.2.2 (at least) handles DMA
to/from addresses above 16MB by buffering data in the kernel.  This
is tunable via the DMAABLEBUF parameter.  I've found that I had to
increase this somewhat to support cartridge tape i/o with INFORMIX-TURBO.
Of course, with MCA or EISA bus, the DMA problems go away.

>Dick Dunn     rcd@ico.isc.com    uucp: {ncar,nbires}!ico!rcd     (303)449-2870

--
Alan Denney # Informix # aland@informix.com # {pyramid|uunet}!infmx!aland

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