View Full Version : Should I choose 64bit (x86_64) or 32bit (i386)?

8th May 2008, 09:55 PM
General Information

You've probably heard these before - 16bit, 32bit, 64bit - But what's it all about? In short, 64bit computer offers several advantages over 32bit because not only is it completely backwards compatible, but you'll find great performance benefits when crunching through large amounts of data (ie video transcoding) and you are able to address larger amounts of RAM (4GB+).

The Technical Stuff

16bit, 32bit, 64bit are all computer architectures. This means that, for example, in 32bit computing the computer deals with integers, registers and memory addresses 32bits in length. 64bit computing, on the other hand, deals with integers, registers and memory addresses 64bits in length. This doesn't sound too exciting, but it allows for a great deal of things. 32bit integers limit the amount of RAM you can address, so even if you have 8GB installed you'll only be able to use 4GB of it on a 32bit system. 64bit memory addresses are larger, allowing for much more memory to be addressed at once. As well, since registers and integers are larger more data can be processed at once, giving a performance boost when processing lots of data.

Instruction sets are the standardized set of commands that a processor can execute. The x86 instruction is associated with the 32bit architecture, however a few years ago it was extended to support 64bits by AMD. This extension is known as x86_64 or x64.

An important note

You'll find that the Fedora packages and/or ISO names use i386, i585 and i686 - There are all names for various generations of Intel processors, which are based on the x86 instruction set. A trick to remember: no matter what X is, iX86 is always x86 (32bit)!

The disadvantages

While the x86_64 platform offers many advantages, it does have some disadvantages. Some applications don't work so well under the 64bit architecture, so you're required to install the 32bit application instead. It will run just fine, however it will pull in all the dependencies with it. In many cases, you'll have two versions of a RPM installed at once - One 32bit (i386) and the other 64bit (x86_64). This takes up roughly 1.5x the disk space of a x86 install. It's also worth mentioning that since the integers and registers are larger compared to 32bit integers and registers, you'll consume slightly more RAM. Don't forget that you get performance boosts in return though! It's also worth mentioning that as 64bit OSs are becoming more popular and the support for x86_64 grows, these problems are less and less apparent.

Is my processor 64bit capable?

Before you download 64bit/x86_64 Fedora, ensure you processor supports the 64bit instruction set:

Most, if not all AMD processors are 64bit capable. If you'd like to be absolutely sure, you can check AMD's website. If you have a Athlon 64 or Opteron processor, it is 64bit capable.
Only certain Intel processors are 64bit capable. To check if your model supports x86_64, check the CPU flags for the EM64T or the lm[b] flag.
Here is how to identify your processor and its flags on various platforms:
Linux: Execute "[b]cat /proc/cpuinfo | grep -e flags -e "model name" | uniq"
Windows: Use the CPU-Z (http://www.cpuid.com/cpuz.php) utility
Mac OS X: Any Mac with a Intel processor will support x86_64. The PowerPC G5 processors also support 64bit computing but with ppc64 instead of x86_64.

As well, be sure to read the Fedora Release Notes (http://docs.fedoraproject.org/release-notes/) for the version you intend to install to ensure your processor and RAM meets the minimum requirements.

Tips & Tricks for x86_64 users

Both Adobe and Sun Java have x86_64 plugins - there's no longer any need for the browser plugin wrapping!