This article describes the calling conventions used when programming x86 architecture microprocessors.

Calling conventions describe the interface of called code:

This is intimately related with the assignment of sizes and formats to programming-language types. Another closely related topic is name mangling, which determines how symbol names in the code are mapped to symbol names used by the linker. Calling conventions, type representations, and name mangling are all part of what is known as an application binary interface (ABI).

There are subtle differences in how various compilers implement these conventions, so it is often difficult to interface code which is compiled by different compilers. On the other hand, conventions which are used as an API standard (such as stdcall) are very uniformly implemented.

The standard for IBM PC compatibles was defined by the Intel processors (8086, 80386) and the literal hardware IBM shipped. Hardware extensions and all software standards (save for a BIOS calling convention) were thrown open to market competition.

A multitude of independent software firms offered operating systems, compilers for many programming languages, and applications. Many different calling schemes were implemented by the firms, often mutually exclusive, based on different requirements, historical practices, and programmer creativity.

After the IBM compatible market shakeout, Microsoft operating systems and programming tools (with differing conventions) predominated, while second-tier firms like Borland and Novell, and open-source projects like GNU Compiler Collection (GCC), still maintained their own standards. Provisions for interoperability between vendors and products were eventually adopted, simplifying the problem of choosing a viable convention.

In these types of calling conventions, the caller cleans the arguments from the stack (resets the state of the stack just as it was before the callee function was called).