How FreeBSD manage more than 4GB on 32 bits architecture

Nguyen Binh binhtien1162 at
Sun Apr 12 03:39:40 UTC 2015

2015-04-09 20:16 GMT+07:00 Lowell Gilbert <
freebsd-questions-local at>:

> Pierre-Yves Péneau <Pierre-Yves.Peneau at> writes:
> > For my internship, I have to find a way to manage more than 4GB of
> > memory with 32 bits processors. It seems that the FreeBSD kernel is the
> > perfect candidate for that. According to the architecture handbook(*),
> > "FreeBSD could theoretically handle memory configurations up to 8TB on a
> > 32 bit platform."
> This is quoting the Architecture Handbook's KVM memory mapping section. The
> following sentence reads "However, since most 32 bit platforms are only
> capable of mapping 4GB of ram, this is a moot point."
> > For the last two days, I was looking for documentation, articles,
> > thesis, or e-mails on that topic, but I can't find relevant
> > informations. Is anybody have informations on that topic ? Where should
> > I start to read the source code to find my answers ?
> I'm going to guess that the idea behind that comment is that FreeBSD's page
> tables can hold 2G (2^31) entries. At a 4k page size, that would give you
> 8TB of memory. But that only helps you if the hardware is physically
> capable of reading from more than 4G different locations.
> Therefore, the question becomes: what kind of hardware are you going to use
> that can keep track of those locations?
> As a side note, I would also recommend the book "The Design and
> Implementation of the FreeBSD Operating System," now out in a new edition.
> Good luck.
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