The Nec APC III appears to be the U.S. version of the NEC PC-9801, which was made in a variety of configurations.
This machine was partially IBM PC compatible, but neither the PC bus or BIOS were cloned. It had an NEC 7220 graphics chip which was not directly CGA compatible, but was much higher resolution, and quite fast for its day.
The CPU is an 8086 running at 8 MHz with 128K of memory. The system used an OEM version of MS-DOS 2.11, modified to work with its non-standard BIOS and hardware. Simple DOS applications that did not make use of IBM BIOS calls or of lower-level hardware would work.
Optionally there was an expansion board called SLE (for Software Library Expander) which some nicknamed the SLEeze board. This board included a second 8086 processor, Phoenix BIOS and memory. In conjunction with its accompanying software this board allowed for "more PC compatibility" by emulating a true PC clone with CGA graphics. Accounts of how well this actually worked vary.
NEC also ported a version of System III UNIX and released it as PC-UX available as an optional OS. NEC also provided a hardware-based virtual memory paging board for PC-UX which helped performance.
Other options included a 10MB hard drive. Memory was expandable to 640K.
Thanks to Richard Bramante for information and pictures.
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