4GB is actually usable, but requires PAE which expands the address space of
a 32-bit Pentium-Pro or later to 64GB. Unfortunately, PAE requires specific
operating system support, and in the Microsoft world, is only on 2k3 server
and, maybe, NT4. XP does not support PAE, neither does Vista-32. Win2k
might.
On Nov 13, 2007 9:00 PM, STeve Andre' <andres@msu.edu> wrote:
> On Tuesday 13 November 2007 21:52:05 Aryeh Goretsky (home) wrote:
> > Hello,
> >
> > I don't think the 3GB limitation there is something specific to
> ThinkPads.
> >
> > Under the IBM PC x86 hardware architecture, pretty much all of the
> > expansion devices in a computer (PCI, AGP and PCIe busses, devices like
> > serial and parallel ports and even keyboards) communicate by mapping
> > (associating) a memory address (or range of memory addresses) to a
> > particular device in order to communicate with it. The operating system
> > and the device drivers provide an abstracted (higher-level) interface to
> > the device, so you can print something by sending it to the LPT1: device
> > instead of having to write a tiny assembly language program to send data
> to
> > 0x378-x037F in order for it get printed.
> >
> > As you install various devices in a computer, such as a video card in a
> > desktop system, the computer has to allocate (reserve) some of the
> memory
> > address space for communicating with the device. For example, a video
> card
> > with 256MB of dedicated video memory would require 256MB of address
> space
> > from somewhere in the 4GB of memory address space available to
> (addressable
> > by) a 32-bit CPU. This also explains why a 32-bit computer with 4GB of
> RAM
> > in it typically reports that less than 4GB of RAM is installed in it:
> The
> > "missing" memory's address space is just being used to communicate with
> the
> > computer's hardware and any actual DRAM memory at those addresses mapped
> > out and inaccessible. Please note this is not the same as the "on
> board"
> > video cards integrated into the motherboard's chipset or commonly used
> in
> > notebooks. Those allocate a block of the computer's on-board DRAM for
> > framebuffer. When you see a computer that reports it has 8MB, 64MB or
> > some-other-recognizable- as-a-power-of-two amount of memory missing from
> > the total amount installed that is typically where it disappeared to.
> >
> > At least, I think that's how it works.
> >
> > I would imagine the same thing occurs under Linux, BSD, OS/2 and other
> x86
> > OSes but am unsure. Perhaps one of the list members who is more
> familiar
> > with these can share their experience?
> >
> > On a semi-related subject, I did note that a company called Emperor
> Linux
> > <http://www.emperorlinux.com/mfgr/lenovo/> sells ThinkPads pre-loaded
> and
> > pre-configured with different 32-bit and 64-bit versions of Linux.
> >
> > Regards,
> >
> > Aryeh Goretsky
>
> Quite right. An OpenBSD system sees about 3,220,439,040 bytes, or 3G.
>
> For more info look at http://www.dansdata.com/askdan00015.htm
>
> --STeve Andre'
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> http://stderr.org/cgi-bin/mailman/listinfo/thinkpad
>
-- - Alex Austin Circuitsoft Computer Services (651) 238-9273 www.circuitsoftcs.com "...and then I visited Wikipedia ...and the next 8 hours are a blur." _______________________________________________ Thinkpad mailing list Thinkpad@stderr.org http://stderr.org/cgi-bin/mailman/listinfo/thinkpadReceived on Tue Nov 13 23:07:07 2007
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