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Speed/Security? Why should we choose to use 64 bit instead of 32 bit?

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Who told you that is is better? Both has advantages and disadvantages. It all depends on what you use your computer for. – Marco Jul 19 '12 at 12:14
possible duplicate of Should I install 32 or 64 bit? – Gilles Jul 20 '12 at 1:45
up vote 4 down vote accepted

Main advantages amd64 over i386

  • 64-bit integer capability
  • additional registers
  • additional XMM (SSE) registers
  • larger physical address space in legacy mode
  • SSE/SSE2

for more details look at wiki page.

What about performance?

Actually performance will grow up to 20-30% in general case. Its mainly due to intelligent compilers that can optimize even non-optimized code for new architecture (mainly due to SSE/SSE2 usage instead of FPU).
PS. In 2009 phoronix made research about this issue. Here it is.

Additional features

In many tools now you can use arithmetic operations while it was too expensive in 32bit system. For example your ifconfig's traffic counter won't reset after 4G level anymore itself (except reboot).

Possible troubles

The main problem is proprietary software. In case software developer spread their product only in binary for 32bit you may have a lot of problems. Sometimes it is possible to find workaround. And hopefully in the GNU/Linux world most of widely used software is open source.

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The main benefit to 64-bit systems is the increased memory address space which is limited to 4GB with 32-bit systems.

This question on the Superuser SE might be helpful: 32-bit vs. 64-bit systems.

Also, here's an informal exploration of 32-vs-64 bit OSes on LifeHacker (though it focuses on Windows, much of it applies I think)

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+1. As a very general rule of thumb, are probably better off running 64-bit if you have more than 3GB. See en.wikipedia.org/wiki/3_GB_barrier. If you have less than 3GB you're probably better off with 32-bit. – bahamat Jul 19 '12 at 17:37
@bahamat I always knew that with XP for instance I couldn't get past 3GB, but always a bit confused because of the stated 4GB limit. I know 2^32 = 4GB, is it the OSes that limits the space to 3GB? – Levon Jul 19 '12 at 17:47
as is often the case, "it depends". Mac OS X has the 3GB limit on 32-bit and Linux must be compiled with PAE enabled to avoid it. Reasons pro and con 64-bit have mostly been mentioned already so I just wanted to point out a quick and easy "If unsure, do this". – bahamat Jul 19 '12 at 18:10
@bahamat Thanks .. I'm certainly happy to be able to make use of all the 8GB RAM on my 64-bit system now :) – Levon Jul 19 '12 at 18:13
@Levon OSes reserve a portion of the address space for internal use. Traditionally in 32-bit systems, they reserved the upper 2 GiB of the 32-bit address space, then the upper 1 GiB and some even the upper 512 MiB only. Some reservation is however required for technical reasons, so even when the OS uses 32-bit linear addressing you don't get to use the full 32-bit address space for your own (applications') benefit. Similar to how the good ol' IBM PC and MS-DOS reserved the upper 384 KiB of the 8086's 1 MiB address space for various system uses, leaving applications to run in the lower 640 KiB. – Michael Kjörling Jun 25 at 12:33

Some 64-bit programs, such as encoders, decoders and encryption software, can benefit greatly from 64-bit registers, while the performance of other programs, such as 3D graphics-oriented ones, remains unaffected when switching from a 32-bit to a 64-bit environment.

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