I have p4 with 512 mb ram,40 gb hard disk...i want to install linux from live cd..for this i have to download iso image..there are some options in the download option..like i686 and X86_64 option...which one sould I download..i want to install desktop version..I want to know the differences also
x86_64 is the 64bit installation for a x86 architecture. I guess this won't work in your case. i686 is for a x86 32bit architecture. more about this and (i368, i486...) can be found here: http://www.sandpile.org/
If your CPU has x86_64 support then either i686 or x86_64 Linux will work. If your CPU lacks x86_64 support then only i686 will work.If both work, 512MB is low enough that the disadvantages of x86_64 for small amounts of ram might be enough of a factor to affect the decision . 40GB hard disk is also low enough to notice the extra disk space needs of x86_64 but not low enough to force the decision of i686.