Editing Wang Laboratories (section)

===IBM-compatible Wang PCs===
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Wang released an emulation board for Wang PC that enabled operation of many PC-compatible software packages. The board accomplished this by monitoring all I/O and memory transactions (visible in those days before [[Northbridge (computing)|North]]/[[Southbridge (computing)|South]] bridge chips to any board plugged into a slot on the expansion bus) and generating a [[non-maskable interrupt]] (NMI) whenever an operation was deemed to involve an incompatible device, requiring emulation.

For example, the floppy controller circuitry on the Wang PC was similar to that of the IBM PC but involved enough design differences that PC-compatible software attempting to manipulate it directly would fail. Wang's PC emulation hardware would detect I/O and memory operations involving the addresses associated with the floppy controller in the IBM PC and generate an NMI. The NMI handler would be activated (the exception vector having been appropriated during system init to point to ROM routines on the emulation board instead of the NMI routine in the PC BIOS) and would then update an internal representation of the IBM PC floppy controller and manipulate the real controller to reflect its state. Reads were satisfied in a similar way, by forcing an NMI, decoding the machine code indicated by the instruction pointer at the time of the fault, and then obtaining the desired info and updating the CPU registers accordingly before resuming the executing program.

IBM PC-emulation on the 8086-based Wang PC was working well when IBM released their 80286-based PC-AT, so Wang made the 80286-based '''Wang APC''' (Advanced Professional Computer).

Further iterations of the PC line were released commencing with the model number PC-240. They booted into MS-DOS or another compatible operating system, and supported [[Industry Standard Architecture|ISA]]-standard expansion cards.

This PC-240 was still not IBM PC-standard, as the keyboard, although a standard PC/AT device, supported VS-compatibility with 24 function keys rather than the normal 12, and had a number of Wang VS-specific keys. There was also a slight difference in CPU interrupts from IBM standard, so some software had compatibility issues.

VS connectivity was via an ISA-based VS-terminal card, or via LightSpeed, the networked VS Terminal Emulator, over an [[IPX]]-based Ethernet connection. The PC-240 came with a Wang-specific [[Hercules Graphics Card]] and compatible screen, which also acted as a keyboard extension, so that the base unit could be kept some distance from the screen. This was later replaced with an [[Enhanced Graphics Adapter|EGA]] card and screen.

Around 1991, Wang released the PC350-16 and PC350-40, which were Intel [[80386]]-based, clocked at 16&nbsp;MHz and 40&nbsp;MHz. They used the same VS-compatible keyboard as the PC-240, had a maximum of 4&nbsp;megabytes of RAM, and came with VGA screens as standard. They were supplied by Microsoft with MS-DOS and Windows 3.0.

The 350-16 had a bug where the machine would freeze and not boot up if power-cycled at the mains. Although it would power on, the BIOS would not start. The solution was to turn on the machine at the mains and hold down the power button for 30 seconds, at which point it would start. It was suggested{{by whom|date=November 2013}} that this was due to an under-valued capacitor in the power circuit. This problem appeared to be resolved in the 350–40, which had a different [[power supply|PSU]].

In 1992, Wang marketed a PC-compatible based on the Intel [[80386SX]] processor, which they called the Alliance 750CD. It was clocked at 25&nbsp;MHz and had a socket for an [[80387]] math coprocessor. It came with 2&nbsp;megabytes of installed RAM, and was expandable to 16 megabytes using [[SIMM]] memory cards. It had a 1.44 megabyte floppy disk drive, an internal 80 megabyte hard disk, and a CD-ROM drive. Five expansion slots were built-in. It came with MS-DOS and Windows 3.1 operating systems.

In 1994, Wang released the slimline Alliance 750CD [[80486]] based PC in the United Kingdom. These machines used standard PC/AT keyboards and were IBM compatible, shipping with MSDOS 5.0 and Windows 3.11 as standard. System [[Nonvolatile BIOS memory|BIOS settings]] and the [[real-time clock]] were maintained by four standard [[AA batteries]] instead of a specialty battery pack or [[lithium battery]]. While offered with a 33&nbsp;MHz [[80486DX]], the 750CD could be upgraded to later [[Socket 3]] processors such as the [[80486DX2]] through the use of third party CPU upgrade adapters or [[interposer]]s. This allowed upgrading to speeds beyond 50&nbsp;MHz without [[overclocking]], or more than 100&nbsp;MHz with overclocking, dependent on the processor used.