For application developers using Oracle Solaris the major difference between the 64-bit and 32-bit operating environments is the C data type model used. The 64-bit version uses the LP64 data model where long and pointers are 64-bit. All other fundamental data types remain the same as in the 32-bit implementation. The 32-bit implementation is based on the ILP32 data model in which int, long, and pointers are 32-bit values. For more information about these models, see Comparing 32-bit Interfaces and 64-bit Interfaces.
All new applications must be developed as 64-bit applications and many of the existing 32-bit applications might require conversion to 64-bit. You might want to convert applications with the following characteristics:
Can benefit from more than 4 gigabytes of virtual address space
Are restricted by 32-bit interface limitations
Can benefit from full 64-bit registers to do efficient 64-bit arithmetic
Can benefit from the performance improvement that the 64-bit instruction set provides
Can benefit from the use of large file awareness
Must run after January 2038
Can benefit from the use of 64-bit time_t that can handle dates for billion years into the future
Read and interpret kernel memory through the use of libkvm, /dev/mem, or /dev/kmem
Use a library that has only a 64-bit version
Access files from a Network Attached Storage (NAS) filer that uses file inode values greater than 32-bit