This appendix describes some special behaviors which vary from operating system to operating system. This is described in table (I.1). The GCC saved registers indicates what registers are saved when certain declaration modifiers are used.
| Operating systems | Min. param. stack align | GCC saved registers |
| Amiga | 2 | D2..D7,A2..A5 |
| Atari | 2 | D2..D7,A2..A5 |
| BeOS-x86 | 4 | ESI, EDI, EBX |
| DOS | 2 | ESI, EDI, EBX |
| FreeBSD | 4 | ESI, EDI, EBX |
| linux-m68k | D2..D7,A2..A5 | |
| linux-x86 | 4 | ESI, EDI, EBX |
| MacOS-68k | D2..D7,A2..A5 | |
| NetBSD-x86 | ESI, EDI, EBX | |
| NetBSD-m68k | D2..D7,A2..A5 | |
| OS/2 | 4 | ESI, EDI, EBX |
| PalmOS | 2 | D2..D7,A2..A5 |
| QNX-x86 | ESI, EDI, EBX | |
| Solaris-x86 | 4 | ESI, EDI, EBX |
| Win32 | 4 | ESI, EDI, EBX |