Why is the RHEL 5 default for applications 32-bit and the SLES 11 default 64-bit?
Historically, the default compilation mode for applications has been -m32 (32-bit) mode to ease the transition from previously existing 32-bit ecosystems. That 32-bit default approach continued from SLES9 to SLES10, from RHEL4 to RHEL5, and continues on the most recent Advance Toolchain 2.1 release. Of course, it is easy to over-ride the 32-bit default and build 64-bit applications. Now that 64-bit applications are becoming more of the norm, the default compilation mode is slowly beginning to change to 64-bit (ie: -m64) moving forward. This started with SLES11. We expect the next version of Advance Toolchain will change its default to 64-bit. It is logical that the next version of RHEL would likely move to a 64-bit default. So if you’re compiling on both SLES 11 and RHEL 5, you’ll observe two different defaults – SLES 11 being 64-bit default – and RHEL 5 being 32-bit. For legacy applications, this can a bit of a nuisance. • Therefore, with gcc and the IBM XL compilers, we always recomm
