Zilog Z80000


The Z80000 is Zilog's 32-bit processor, first released in 1986. It is essentially a 32-bit expansion of its 16-bit predecessor, the Zilog Z8000. It includes multiprocessing capability, a six-stage instruction pipeline, and a 256-byte cache. Its memory addressing system can access 4 gigabytes of RAM. Described at the time as a "mainframe on a chip", the processor is in many ways an equivalent to Intel's 80386. It can execute code written for the Z8000, but is not compatible with the Z80.
Sixteen general-purpose registers of variable size are available through use of a 64-byte "register file". The processor includes a memory management unit that provides protected memory, important for multitasking, and virtual memory addressing for temporary storage of RAM on a hard disk. The processor has three methods of accessing memory:
The processor is designed to interoperate with other integrated circuits designed for use with the Z8000, such as the Zilog Z8070 floating-point coprocessor.
The Z320 was the CMOS version of the Z80000.

Linear vs. Segmented Addressing

Linear addresses used the complete result of any address computations, and so could address any part memory without restriction.
Segmented addresses restrict effective address computations to the specified segment of the base pointer register. For example, if RR2 contained the value 0x10002000, and you wanted to access a byte offset 0xE000 from this pointer, the final effective address would be 0x10000000, as the wrap-around into higher address bits is prevented. Base address bit 31 selects whether 64KiB segments or 16MiB segments are used. Note that the base address register determines the segment size and number.
Segment in this case refers not to an Intel-style segment, but to a Unix-style segment.