Output operations to the printer may go either to a local printer or to a file for subsequent printing, so a buffer which can be unloaded to either destination emulates the PC printer. An input/output processor handles I/O operation requests of the emulating processor, using the host system I/O devices to emulate some of the PC I/O devices. The display updates of the emulating processor are detected and provide information for the host processor in updating a part of its display which provides the information a PC display would provide simultaneously with the display characteristic of the host system. The memory accesses of the emulating processor are mapped into the host system memory, so that the host processor is protected from defective PC software on the emulating processor. Circuitry monitors the emulating processor outputs and provides information to the host system so that it can emulate the environment of the PC CPU, emulating both memory and I/O devices. The emulating processor executes sequences of instructions executable by a PC being emulated, but a host processor independently executes sequences of its instructions which are different from PC instructions. Abstract: An emulating data processor includes a host system and an emulating processor with outputs to and inputs from the host system.
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