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From: veit@borneo.gmd.de (Holger Veit)
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: 19 May 1994 22:40:46 GMT
Organization: GMD
Lines: 38
Message-ID: <2rgpte$ia8@omega.gmd.de>
References: <VIXIE.94May19144247@office.home.vix.com>
NNTP-Posting-Host: borneo.gmd.de
X-Newsreader: Tin 1.1 PL5
Paul A Vixie (vixie@vix.com) wrote:
: jesus, you ignorant s**thead, i made the mistake of running a newsreader
: that doesn't have any KILL files installed, and i happened to glance
: accidentally at one of your articles today.
Hope you find a better newsreader soon :-)
: > As you may (or may not) know, many early version of the Intel 386
: > could not handle more than 16MB of memory. Along with this
: > many "support chips" could not support the address lines to
: > use ">16 MB" of memory.
:
: 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.
:
I understand that you and many others (including me) don't like the
words JM emits. But unfortunately this time you missed the point.
Actually, several older 386 chipsets that were slightly modified 286
chipsets HAD problems with >16MB (mostly problems related to refresh).
Today, it is not uncommon even on ISA motherboards to handle more than
16MB RAM. The 386 has 32 address lines, and thus can address 4GB.
The point is: this is on-board RAM that is almost directly connected
to the processor address pins (drivers and multiplexors ignored).
The ISA bus is not involved here, so the 24bit limit is void here.
The ISA bus IS however involved in bus-mastering DMA,
which is a sort of an external access from a card in a slot to the
on-board memory. From there it is impossible to access more than 16MB
through ISA because of the 24 address lines (without multiplexing).
--
Dr. Holger Veit | INTERNET: Holger.Veit@gmd.de
| | / GMD-SET German National Research | Phone: (+49) 2241 14 2448
|__| / Center for Computer Science | Fax: (+49) 2241 14 2342
| | / Schloss Birlinghoven | Had a nightmare yesterday:
| |/ 53754 St. Augustin, Germany | My system started up with
| ... Booting vmunix.el ...