Re: [Thinkpad] New Thinkpad -- help with turbo memory&driveselection...

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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Received on Tue Nov 13 22:00:57 2007