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Re: Do I need 64Bit if RAM is more than 4 GB?

On Wed, 2004-09-08 at 08:23 -0400, Lennart Sorensen wrote:
> On Wed, Sep 08, 2004 at 02:29:09AM -0500, Ron Johnson wrote:
> > I'd say "hack" is a strong word for PAE, which is just an extension
> > of the segmented memory concept.
> I think intel's messy segmented memory model is quite a hack.  At least
> with the 386 in protected mode you could treat memory as flat (except
> for that hole at 640 to 1024k, but you could just start at 1M and forget
> about it).  With PAE now you are back to having segments and mapping and
> such going on again.  Having done a bit mf programing at the OS level on
> a 486, I sure felt like intel's memory segments were a hack, which even
> made the pagetables in protected mode somewhat messy to create.

Back when segments were 16 bits wide, yes it was a pain.  I'm old
enough to have done assembly programming on the 8088.  (Now that I
have the wisdom of time, I understand why Intel did what they did,
even though the 68K was much cleaner.)

Now (actually since the 386), though, the segments are 32 bits 
wide, and the need to manipulate segments has migrated into the
kernel, while each userland app sees a 32 bit address space.  To
me, that's an acceptable compromise.

In fact, it seems to me that *any* 32 bit processor (SPARC, HPPA,
Power) that wants to be able to use more than 4GB of total RAM
would have to use such a segmentation scheme.

Ron Johnson, Jr.
Jefferson, LA USA
PGP Key ID 8834C06B

NAMBLA - Nat'l Assoc of Marlon Brando Look-Alikes (Yes, it's a
South Park reference.)

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