Zilog Z8000

The Z8000 is a 16-bit microprocessor introduced by Zilog in early 1979. The architecture was designed by Bernard Peuto while the logic and physical implementation was done by Masatoshi Shima, assisted by a small group of people. In contrast to most designs of the era, the Z8000 did not use microcode which allowed it to be implemented in only 17,500 transistors. The Z8000 is not Z80-compatible, but it uses many of the well-received design elements from the Z80. Among these is the ability for its registers to be combined and used as a single larger register; while the Z80 allowed two 8-bit registers to be used as a single 16-bit register, the Z8000 expanded this by allowing two 16-bit registers to operate as a 32-bit register, or four to operate as a 64-bit register. These combined registers are particularly useful for mathematical operations. Although it saw some use in the early 1980s, it was never as popular as the Z80. It was released after the 16-bit Intel 8086 (April 1978) and the same time as the less-expensive Intel 8088, and only months before the Motorola 68000 (September 1979), which had a 32-bit instruction set architecture and was roughly twice as fast. The Zilog Z80000 was a 32-bit follow-on design, launched in 1986. The Z8000 initially shipped in two versions; the Z8001 with a full 23-bit external address bus to allow it to access up to 8 megabytes of memory, and the Z8002 which supported only 16-bit addressing to allow 64 kilobytes of memory. This allowed the Z8002 to have eight fewer pins, shipping in a smaller 40-pin DIP format that made it less expensive to implement. The series was later expanded to include the Z8003 and Z8004 updated versions of the Z8001 and Z8002, respectively. These versions were designed to provide improved support for virtual memory, adding new status registers to indicate segmentation faults (test and set) and provide an abort capability. There are sixteen 16-bit registers, labeled R0 through R15. The registers can be concatenated into eight 32-bit registers, labeled RR0/RR2/.