The ability to handle larger amounts of data directly in physical memory rather than relying on disk I/O is perhaps the most significant performance benefit of 64-bit machines. However, some applications compiled in 32-bit mode perform better than when they are recompiled in 64-bit mode. Some reasons for this include:
Some ways to compensate for the performance liabilities of 64-bit programs include:
double preTax(double total) { return total * (1.0 / 1.0825); }
will perform faster than the more straightforward:
double preTax(double total) { return total / 1.0825; }
The reason is that the division (1.0 / 1.0825) is evaluated once, and folded, at compile time only.