What's the difference between i386 & i686?
 

Both of my laptops (Dell Latitude C640 & D610) have i386 processors, or whatever the i386 means. Between the two, I have four Linux distros, Linux Mint (Gloria), PCLinuxOS, Ubuntu 9.04 and Xubuntu 9.04. When I updated Firefox (by the command line), some of them reports that it's a i686 browser. With Windows, I always had the latest Firefox, and the command line was the only way that I could see to upgrade. Will these i686 browsers mess up my laptop in any way? I hope not, because I want the fastest possible browsers on my laptop. Firefox 3.0.4 (or whatever) is too slow for someone that is used to speed. By the way, I love Linux, and like to use different distros. And I especially love the freedom of no hassles on installation and can update when I want to. On both of these laptops, only a small partition (the first one) is reserved for Windows. That's also where most of my drivers are. I still need Windows for printing, but that's about all. My main concern is these i686 browsers on my i386 system. Any advice or suggestions would be greatly appreciated.

It's not a problem; see the many qns about that here at LQ.
Basically, the i386 architecture is the HW for the Intel 386 (32 bit) processor from a few years back.
In order to maintain backward compatibility, they then came up with the i486, i586, i686 improvements; all of which are i386 compatible.
If you run

uname -a

at the cmd line, it'll mention either those or x86_64, which is their current 64 bit architecture. This however does run i386 etc sw as well. Not all sw is currently avail as native 64 bit, so it runs 32 bit as well.

HTH
http://en.wikipedia.org/wiki/Intel_80386
http://en.wikipedia.org/wiki/Intel_P...rchitecture%29

...

i386 is the old standard i686 is the new
but a i686 program compiled from source will work on the i386 old standard at reduced speed
and a binary or compiled from source i386 program will run on a i686 without any speed redduction