Mailinglist Archive: opensuse (686 mails)

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Re: [opensuse] 64 bit vs 32 bit RAM consumption
  • From: "Carlos E. R." <robin.listas@xxxxxxxxxxxxxx>
  • Date: Tue, 23 Jul 2013 14:44:12 +0200 (CEST)
  • Message-id: <alpine.LNX.2.00.1307231440200.5519@minas-tirith.valinor>
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El 2013-07-23 a las 08:05 -0400, Felix Miata escribió:

In googling the possibility of using a 64 bit kernel on an otherwise 32 bit openSUSE (consensus: don't try it), I found quite a bit of mention of 64 bit apps using twice as much RAM? Is this true? Or is it just misunderstanding arising from 64 bit using twice as many CPU registers to increase its own speed?

It is true, in part. It depends on how the program defines values.

If the programmer knows the maximum value of a variable (if he doesn't, he guesses and sets a limit), he may choose the smaller variable needed to hold it (the other criteria is the one that is faster to access for the architecture). Or he may simply choose a default value, like "integer".

However, when the application was designed for 32 bit and then is re-compiled for 64, it may well happen that the size of the variable types chosen may shift from 32 to 64 bit - thus automatically the size of those variables increase to double.

If that data space is large, the impact can be significant.

Yes, it is a bug.

FWIW, not all RAM is "cheap".

Oh, absolutely. I upgraded my previous machine because I could not find RAM at a reasonable price. My advice is to upgrade machines RAM to the maximum when that RAM is still manufactured in large quantities. Later, availability decreases and price increases.

- -- Cheers

Carlos E. R.
(from 11.4, with Evergreen, x86_64 "Celadon" (Minas Tirith))
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