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Computing (FOLDOC) dictionary
Zilog Z8000
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processor A microprocessor from Zilog introduced not
long after the Intel 8086, but with superior features. It
was basically a 16-bit processor, but could address up to 23
bits in some versions by using segment registers (to supply
the upper 7 bits). There was also an unsegmented version, but
both could be extended further with an additional MMU that
Internally, the Z8000 had sixteen 16-bit registers, but
register size and use were exceedingly flexible. The Z-8000
registers could be used as sixteen 8-bit registers (only the
first half were used like this), sixteen 16-bit registers,
eight 32-bit registers, or four 64-bit registers, and included
32-bit multiply and divide. They were all general purpose
registers - the stack pointer was typically register 15,
with register 14 holding the stack segment (both accessed as
one 32-bit register for painless address calculations).
The Z8000 featured two modes, one for the operating system
and one for user programs. The user mode prevented the user
from messing about with interrupt handling and other
potentially dangerous stuff.
Finally, like the Zilog Z80, the Z8000 featured automatic
DRAM refresh circuitry. Unfortunately it was somewhat slow,
but the features generally made up for that. Initial bugs
also hindered its acceptance (partly because it did not use
microcode). There was a radiation resistant military