A processor made by Western Digital, consisting of at least four separate integrated circuits, including the control circuitry unit, the ALU, two or four ROM chips with microcode, and timing circuitry.
The ALU chip contained twenty-six 8-bit registers and an 8-bit ALU, while the control unit supervised the moving of data, memory access, and other control functions. The ROM allowed the chip to function as either an 8- or 16-bit chip, with clever use of the 8-bit ALU. Further, microcode allowed the addition of floating-point routines (40 + 8 bit format), simplifying programming (and possibly producing a floating-point coprocessor).
Two standard microcode ROMs were available. This flexibility was one reason it was also used to implement the DEC LSI-11 processor as well as the WD Pascal Microengine.