I may be stating the obvious, depending on what you know, but as far as I understand it goes something like this: Info goes to the cpu of a 32 bit machine in chunks of, you guessed it: 32 bits. Obviously with 64 bit machines it's 64 bit chunks, but the interesting thing is that many if not all 64 bit chips can recognize when they get chunks of 32 bit code, and emulate. I think that the gcc64 use flag means that you will compile your kernel in 64 bit code. That may mean that you compiled your kernel with a 32 bit compiler before. Now considering you're on the gentoo-amd64 forum, I assume you have x86_64 gentoo and that your arch is set to x86_64, so the use flag seems a bit redundant to me. I'm probably wrong, I have no experience with this, it's late, I'm tired. Please, someone correct me if I'm just being an idiot, or if that's not the question you asked. In the unlikely event that I'm right, here would be some pro's and cons. You may not be fully unlocking the potential of your shiny new 64 bit machine by using a 32 bit kernel. The pro would be that you may (not sure, depends on what your kernel is before you recompile) be able to use 32 bit software. Many closed source programs and some programs that emulate the closed source stuff are in 32 bit, and have trouble in 64. I think you'd only run into trouble with java and flash using 64 bit kernel. Adobe still doesn't offer 64 bit flash to my knowledge, and java is a bit of a pain in any flavor. Again, I may be just babbling, and if I spent this e-mail regurgitating things that you already know, I apologize. That was my interpretation, hope it helped. -Peter On 12/27/06, Simon Stelling wrote: > > Robert Cernansky wrote: > > Can anybody explain more? What are the pros and cons to switch it > on/off? > > The USE flag is only effective on ppc64 and sparc where the kernel > sometimes is the only code that is compiled 64bit and therefore a > seperate, much smaller version of gcc is used to build the kernel. The > flag should in fact be masked everywhere except for those profiles, > which is what bug 144535 [1] deals with. > > [1] http://bugs.gentoo.org/show_bug.cgi?id=144535 > > -- > Kind Regards, > > Simon Stelling > Gentoo/AMD64 Developer > -- > gentoo-amd64@gentoo.org mailing list > >