invalid function numbers, or valid function numbers with invalid values of key parameters—particularly with an early IBM BIOS version—the BIOS may do nothing and return with no error code; then it is the [inconvenient but inevitable] responsibility of the caller either to avoid this case by not making such calls, or to positively test for an expected effect of the call rather than assuming that the call was effective. Because BIOS has evolved extensively in many steps over its history, a function that is valid in one BIOS version from some certain vendor may not be valid in an earlier or divergent BIOS version from the same vendor or in a BIOS version—of any relative age—from a different vendor.) Because BIOS interrupt calls use CPU register-based parameter passing, the calls are oriented to being made from assembly language and cannot be directly made from most high-level languages (HLLs). However, a high level language may provide a library of wrapper routines which translate parameters from the form (usually stack-based) used by the high-level language to the register-based form required by BIOS, then back to the HLL calling convention after the BIOS returns. In some variants of C, BIOS calls can be made using inline assembly language within a C module. (Support for inline assembly language is not part of the ANSI C standard but is a language extension; therefore, C modules that use inline assembly language are less portable than pure ANSI standard C modules.) Invoking an interrupt Invoking an interrupt can be done using the INT x86 assembly language instruction. For example, to print a character to the screen using BIOS interrupt 0x10, the following x86 assembly language instructions could be executed: mov ah, 0x0e ; function number = 0Eh : Display Character mov al, '!' ; AL = code of character to display int 0x10 ; call INT 10h, BIOS video service Interrupt table A list of common BIOS interrupt classes can be found below. Note that some BIOSes (particularly old ones) do not implement all of these interrupt classes. The BIOS also uses some interrupts to relay hardware event interrupts to programs which choose to receive them or to route messages for its own use. The table below includes only those BIOS interrupts which are intended to be called by programs (using the "INT" assembly-language software interrupt instruction) to request services or information. : execute BASIC traditionally jumped