On Nov 24, 2010, at 6:27 PM, mcclnx mcc wrote: > Thank you for answer. > > This server used to run under CENTOS 3.9 X86 and No problem. Due to application can not use CENTOS 3.9 we need upgrade to CENTOS 4 or 5. > > If I re-install it and use CENTOS 4.8 X86, will problem gone or not? A few options. You might test the program on a 64 bit OS. The 64 bit version of CentOS should be able to run many 32 bit programs. It would depend on dependencies in the program whether it would have issues or not. In fact, other changes since 3.9 may be more of an issue than the 64 bitness of the OS. It is possible to limit the amount of RAM that the OS will recognize by passing options to the kernel in grub. You also may be able to run a 32 bit version of the OS in virtualization under a 64 bit OS, leaving the rest of the RAM available for the main system. 2 computers in 1.