High memory support in 2.6.15-amd64-server kernel?

Joris Dobbelsteen Joris at familiedobbelsteen.nl
Tue Jan 23 12:35:11 UTC 2007

Hash: SHA256

Read this: http://kerneltrap.org/node/2450

The 32-bit versions on the IA32 of the Linux kernel can only address 1 GB of RAM, because they did one stupid thing in the past. They mapped the entire physical memory into the kernel virtual address space (which is 1 GB, while the user space is 3GB).
Other OSes, such as BSD and Windows don't map the entire physical memory, removing the need for the so-called 'high memory'.

Of course, when the address space gets larger, the limits move too. You can now map the entire RAM into the kernel part again, as its (64-2) bits addressable (not sure, but at least large enough for current common memory sizes).
So you don't need any more 'high memory' support in the upcoming years (decades?).

- - Joris

>-----Original Message-----
>From: ubuntu-users-bounces at lists.ubuntu.com 
>[mailto:ubuntu-users-bounces at lists.ubuntu.com] On Behalf Of Andreas
>Sent: dinsdag 23 januari 2007 11:12
>To: ubuntu-users at lists.ubuntu.com
>Subject: High memory support in 2.6.15-amd64-server kernel?
>I have a HP ML350 with a Xeon 5130 2Ghz CPU and loads of disk. 
>It came with 512Mb RAM so I ordered another 1,5Gb RAM.
>But when I want to set High Memory Support in menuconfig, I 
>don't have the choice? I mean, in "Processor type and 
>features" there is no longer an option called High Memory 
>Support. Has this been taken out or does it
>  have an dependency I've missed?
>ubuntu-users mailing list
>ubuntu-users at lists.ubuntu.com
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