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From: Oliver Kleinke <oliver.kleinke@c-01a.de>
Newsgroups: comp.lang.ada
Subject: Re: Increasing GNAT's heap
Date: Wed, 13 Nov 2013 16:32:13 +0100
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> It is 8GB RAM allowed for the virtual machine.

Probably a waste without PAE.

> Are you sure about 4GB? Doesn't Linux reserve some address space for
> its the kernel? Under Windows, where GNAT has same problems I cannot
> get more than 2GB. There is a boot switch to allow 3GB but it does
> not work well with GNAT. When GNAT is running under 64-bit Windows it
> goes through being 32-bit itself. From this I conclude that true 4GB
> under Linux would be enough to compile it.

Various chunks of the 32-bit address space are used to address
various hardware devices in your machine, e.g. PCI devices, APIC etc.
IIRC, how much address space is "wasted" depends on the hardware. So in
essence you will never get 4GiB of RAM on a 32-bit machine.