hi peter-

"sinclair zx80 computer"
" its many times bigger than an AT89C2051 in size,
power consumption and also in price.
Seems comparing apples and bananas. "

how many chips does it have,and the power consumption is ?
(the sinclair)--my point was
that the product "zx80" is an example of the full utilization of
the features of the z80 and is an incredible work at the
minimumization of hardware with software---for what it can
do in terms of preformance.(do that with the '51)--(if you can
not say the chip count and current consumption,then you
cannot say which is the apple or which is the bannana)

"and the bit manipulation of the z80 is only 240 separate instructions"
But I think, not so easy, fast and small, e.g.:
X = Y or not Z :
X equ P1.0
Y equ P1.1
Z equ P1.2
mov c, Y
orl c, /Z
mov X, c "

how many bytes?
(if you are reading the "pin" you forgot to slap the bits (port)
with 1's)
and how fast?
how easy is recursion?

"then on power up copy the rom into the ram then run on the ram"
Is this a needed feature of a washing machine ? "

this architecture is the absolute most versatile--certainly you
realize this and to have distinct code/data is inhibitive.with
the "restart" instruction of the z80--a clever code writer can
write his own "instructions"..

reg-jack