The Z8000 CPU series was introduced in early 1979, between the launch of the Intel 8086 (April 1978) and the Motorola 68000 (September 1979).
Two versions were released, the Z8001 capable of addressing 8 MB of memory via segment registers, and the Z8002 which could only address 64 KB. Like the Zilog Z80, the Z8000 included built-in DRAM refresh circuitry. An optional Z8010 MMU (Memory Management Unit) co-processor allowed up 48 MB of memory to be addressed.
Internally the Z8000 chip held 17500 transistors in NMOS design, and it had sixteen 16 bit registers which could be extremely flexibly used. The programmer could see them as 16 8-bit, 16 16-bit, 8 32-Bit, or 4 64-bit registers. All registers were general-purpose registers, although registers 14 and 15 were usually used as stack segment and pointer. Among its 110 instructions and 13 addressing modes, the Z8000 also offered 32-bit multiplication and division instructions.
There was both a user mode, for programs, and a supervisor mode, for the operating system. The user mode prevented access to potentially dangerous things such as interrupt handling.
Despite these attractive features the Z8000 was not very fast and suffered from some internal bugs. It was thus never very popular and was surpassed a few months later by the Motorola 68000 and later, by the Intel 286.
The Z8000 can be found in some rare but well-known computers though, such as the Olivetti M20 and M40, and the Unix-based Commodore 900. Some third parties also manufactured the Z8000 including AMD, Hitachi and Sharp.
The Z8000 was followed in 1986 by the Z80000, an amazing 32 bit processor whose features (pipeline, cache memory) would not appear until six years later in Intel processors.
The Z8000 is still alive nowadays with the Z16C00, a CMOS version mainly used in embedded applications.
Mike Throm's memories:
I worked in Zilog's system division for 6 years. The primary goal was to design systems using Zilog processors. One of the notable leaders of Zilog's system engineering group was Judy Estrin who lead the effort to develop an ethernet like LAN product for Zilog, who then went on to other ventures like Bridge Communications (acquired by 3Com), NCD, and Precept.
Zilog also designed a UNIX "supermicro" system called the S8000 initally based on the Z8000, then the Z80000 with a UNIX based OS called Zeus.
Like most silicon valley firms of the time, we took pride in what we did and spent long hours to develop products. 60 - 80 hours per week during peak development cycles were common. Also, because almost all of us were under 30, weekend parties and "beer busts" were also common between development cycles.
Many S8000 units were sold to the IRS; however, the system side of the business never took off and was eventually closed down around 1985.
Peter Sandilands adds:
The Z8000 was used in a quite successful line of computers from Onyx Inc (California). Originally built for AT&T they ran Unix V7 and Interactive Systems IS/1.
The architecture continued into the mid '80s and ran Sys III. Sold as general purpose business computers they had the option of a number of bundled business packages using software such as Quadratron word processor. New Onyx C8002s were still being sold in 1986!