Need of different memory zones

[Prabhu nath]

Read my reply for the related question here.
http://www.spinics.net/lists/newbies/msg43910.html

On Wed, Mar 13, 2013 at 3:16 PM, Niroj Pokhrel <nirojpokhrel at gmail.com>wrote:

> Hi All,
>
> I have been studying Memory Management in linux. But I am confused with
> the division of different ZONE. The use of ZONE_DMA and ZONE_NORMAL is
> fine. But I am confused with ZONE_HIGHMEM, if the system is 32 bit then why
> can't it map 4GB memory (2^32). I had thought that ZONE_NORMAL was for the
> kernel usage so directly mapped and ZONE_HIGHMEM for the user process and
> is not directly mapped to facilitate virtual addressing. But I know I am
> not getting something right. While going through Ch - 15 of Rubini's Linux
> Device Driver (Memory Management and DMA) I came across following line
>
> "a 64-bit architecture such as Intel’s x86-64 can fully map and handle
> 64-bits of memory.Thus, x86-64 has no ZONE_HIGHMEM and all physical memory
> is contained within ZONE_DMA and ZONE_NORMAL."  So, if it can be directly
> mapped why not in 32 bit architecture.
>
> I am really confused. Please Help. Thanking you in Advance
>
>
> Yours,
> Niroj Pokhrel
>
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>


-- 
Regards,
Prabhunath G
Linux Trainer
Bangalore
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