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From: michaelv@iastate.edu (Michael L. VanLoon)
Newsgroups: comp.os.mach,comp.unix.bsd,comp.unix.pc-clone.32bit,comp.os.386bsd.development
Subject: Re: More Details on the 386BSD Release 1.0 CD-ROM
Date: 26 May 94 18:51:42 GMT
Organization: Iowa State University, Ames, Iowa
Lines: 31
Message-ID: <michaelv.769978302@ponderous.cc.iastate.edu>
References: <jmonroyCq1qK0.5vJ@netcom.com> <VIXIE.94May19144247@office.home.vix.com> <2s19rb$77v@acmex.gatech.edu>
NNTP-Posting-Host: ponderous.cc.iastate.edu
In <2s19rb$77v@acmex.gatech.edu> gtd543a@prism.gatech.edu (Jeff M. Garzik) writes:
>In article <VIXIE.94May19144247@office.home.vix.com>, Paul A Vixie <vixie@vix.com> wrote:
>>there are only 24 address lines on an ISA bus. if you know a chip set that
>>can address more than 16MB of memory using those 24 address lines, please
>>tell us all about it.
>My pure-ISA motherboard has 8 SIMM slots instead of the normal 4, and I
>ran 24MB just fine under OS/2. Of course, I don't know what it was
>doing... it may or may not have been using those 24 address lines, I
>dunno. ;-) Just stating a case...
The ISA *BUS* has 24 address lines. The CPU can access up to 4GB of
memory (though most motherboards could never hope to hold that much
RAM). Cards on your ISA *BUS* can NOT access more than 16MB of your
RAM, since they have to use the 24 address lines the ISA bus provides.
EISA and PCI don't have this limitation because they use 32 address
lines (allowing 4GB of physical addressing).
In your case, you probably a) weren't using any hardware that tried to
use DMA in the upper ranges of your memory, and/or b) OS/2 knows not
to try doing DMA over 16MB with ISA devices (can be slower).
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Michael L. VanLoon Iowa State University Computation Center
michaelv@iastate.edu Project Vincent Systems Staff
Free your mind and your machine -- NetBSD free Un*x for PC/Mac/Amiga/etc.
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