## ALP Programming Guide and Reference

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### Description

The PUSH instruction decrements the stack pointer by 2 if the operand-size attribute of the instruction is 16 bits; otherwise, it decrements the stack pointer by 4. The PUSH instruction then places the operand on the new top of stack, which is pointed to by the stack pointer.

The PUSH ESP instruction pushes the value of the ESP register as it existed before the instruction. This differs from the 8086, where the PUSH SP instruction pushes the new value (decremented by 2).

Likewise, a PUSH-from-memory instruction, which uses the stack pointer (ESP ) as a base register, references memory before the PUSH. The base used is the value of the ESP before the instruction runs.