i686 vs x86_64?

What is the difference between i686 vs x86_64?
srikanthradAsked:
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TachionConnect With a Mentor Commented:
The i686 is 32-bit, the x86_64 is 64 bit.

i686 is almost the same as i386, with a few additional operants added. It is the latest 32-bit architecture.
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TachionCommented:
You can find a more detailed explanation on Wikipedia: http://en.wikipedia.org/wiki/P6_(microarchitecture)

The details of the i686 architecture are explained in more detailed. Essentially, the i686 instruction set goes back to the architecture of the "sixth generation" processors, the Pentium Pro. (Yup, it is that old!) After that the instruction set was mostly extended with extensions, such as the SSE instructions and MMX instruction.

Intel tried to go to 64-bit with Itanium, which was not backward compatible with the i686 type processors. AMD instead went with x86_64, which was backward compatible. This is one battle that went to AMD, in the end Intel also took the x86_64 extension to 64 bit, since it was far more successful. Remember, everyone was still using 32-bit operating systems at that time. Please note this is a very (very!) simplified version of what happened.

So, when you want to program for any of the current lines of processors in 32-bit mode, you use i686. If you want 64-bit code, you use the x86_64.
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legolasthehansyConnect With a Mentor Commented:
Adding to the above, you can run 32-bit applications on 64-bit but not 64-bit apps on 32-bit.

Regards,
Lego
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martin_seaConnect With a Mentor Commented:
The x86_64 version is for 64bit processors (Intel based). If you have a x86_64 bit processor its always recommended that you
run a 64 bit OS on it.

i386 = 386 e-processors
i486 = 486 e-processors
i586 = Pentium
i686 = Pentium II and older

PS "i" in the notation emphasizes that the designation of Intel.
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srikanthradAuthor Commented:
Thank you.
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