Missing 1GB RAM, where is it?

[haojian.zhuang@gmail.com (Haojian Zhuang)]

On Fri, Apr 15, 2011 at 12:12 AM, Haojian Zhuang
<haojian.zhuang@gmail.com> wrote:
> On Thu, Apr 14, 2011 at 11:43 PM, Andrzej Kardas <andrzej-kardas@o2.pl> wrote:
>>
>>
>> On 14.04.2011 17:09, Adrian Cornish wrote:
>>
>> Just a thought - lower end graphic cards use system RAM as their own
>> dont they
>>
>> You right, devices like graphic card, ethernet cards etc. are mapped into
>> memory, what cause some amount RAM is not available for system use. But as
>> i've wrote before, i'm wondering why addresses in /proc/iomem (where the map
>> of memory is) are not contiguous. I think, there should be info about what
>> region of memory is mapped where (BIOS, PCI bus, for system use etc) for
>> whole 4GB (Am I right??) address space (for 32bit OS). Instead of that,
>> there are small "holes" in addresses and the total size of this holes (in my
>> case) is about 400MB. So i wonder where that memory is.
>>
> What you see from /proc/iomem is virtual address. For the 32-bit
> system, it's 4GB size.
> Virtual address needn't be sorted one by one.
>
> You have 4GB physical memory. But only a part is mapped linearly in
> virtual address.
> They're called lowmem. The rest are used as highmem what can be
> allocated by device
> driver or applications. Kernel needs to map it first before accessing highmem.
>
> CPU's MMU manages the mapping table between virtual address and
> physical address.
>
Oh, my inputs are wrong. Please ignore it. I messed something. What we saw
should be physical memory. I think the real hardware should be accessed by
36-bit, not 32-bit.
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>