How can I find information about DPMI programming?

In order to alleviate this limitation, instructions like ENTER/LEAVE, or other direct manipulations of the stack register (ESP) can be used for saving local data in the stack. The instruction architecture also includes PUSH/POP instructions for direct usage of the stack for integer and address quantities. This helps simplify ABI specifications with respect to "call stack" software support mechanisms as compared with some RISC architectures which must be more explicit about call stack details.