System and method for emulating the operation of a video graphics adapter

A method for emulating VGA hardware for a guest operating environment in a host operating environment for a computer system, wherein the guest operating environment is operable to send instructions to the VGA hardware, wherein the VGA hardware is configured under a current VGA mode, and is operable to be configured in one of a possible plurality of VGA modes, wherein the current VGA mode is associated with a set of current mode flags, and wherein the computer system comprises a memory, comprising the steps of:

• receiving an instruction issued from the guest operating system and directed to the VGA hardware, wherein the instruction is directed to change the current VGA mode to a new VGA mode;
• generating a set of new VGA mode flags associated with the new VGA mode;
• comparing the current VGA mode flags to the new VGA mode flags;
• providing a jump table, wherein the jump table comprises one or more jump table entries operable for pointing to one or more addresses in memory, wherein the jump table entries are associated with a specific VGA mode, and each jump table entry is associated with a specific instruction in the set of permissible instructions for the specific VGA mode, and wherein the jump table contains the current VGA mode flags;
• determining that there is no significant difference between the current VGA mode flags and the new VGA mode flags, after the step of comparing the current VGA mode flags to the new VGA mode flags;
• and
• maintaining the jump table entries.

A computer-readable medium comprising computer-readable instructions for emulating VGA hardware for a guest operating environment in a host operating environment for a computer system, wherein the guest operating environment is operable to send instructions to the VGA hardware, wherein the VGA hardware is configured under a current VGA mode, and is operable to be configured in one of a possible plurality of VGA modes, wherein the current VGA mode is associated with a set of current mode flags, and wherein the computer system comprises a memory, said computer-readable instructions comprising instructions for:

• receiving an instruction issued from the guest operating system and directed to the VGA hardware, wherein the instruction is directed to change the current VGA mode to a new VGA mode;
• generating a set of new VGA mode flags associated with the new VGA mode;
• comparing the current VGA mode flags to the new VGA mode flags;
• providing a jump table, wherein the jump table comprises one or more jump table entries operable for pointing to one or more addresses in memory, wherein the jump table entries are associated with a specific VGA mode, and each jump table entry is associated with a specific instruction in the set of permissible instructions for the specific VGA mode, and wherein the jump table contains the current VGA mode flags;
• and
• providing a mode table, wherein the mode table comprises one or more mode table entries, wherein each mode table entry is associated with a specific VGA mode and is operable for pointing to one or more addresses in memory.