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Section A:
A.3.7 The Central Unit
General Introduction
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*
Outside the Computer
*
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This
term refers to the mysterious part of your computer
where
every-
thing comes together.
Quite literally so,
because it is here where the
cables
from
the CRT monitor,
the keyboard,
the printer and the
mass
memories
end.
Your MZ-3500 keeps up to two Minifloppy drives
in
this
housing, too.
The central unit consists of the following functional blocks:
- The CPU
In
order to run EOS,
this must be a chip from the Z80 family
(Your
MZ-3500
includes
two
of
such
chips
for
better
throughput).
It
transforms
the
instructions given
in
the
programs into the desired actions and manages the main memory.
That is all you need to remember for now.
- The Main Memory
All you should remember is that the programs are executed from
within the main memory.
EOS also resides here.
Its capabili-
ties are related directly to its size.
As the Z80 can address
only
64
Kbytes directly,
EOS has several memory
management
mechanisms built in,
thus being able to make full use of
the
128 to 256 Kbytes of your MZ-3500.
Data
and programs are stored in the main memory.
Each single
byte
can be directly referred to by the
CPU,
can
be
read,
changed, and stored back again. Its disadvantage is its energy
dependance;
as soon as power is turned off,
its contents get
lost at once.
- The Control Units
These
devices,
some
of them being very
11
intelligent",
are
devoted to control data transfer to and from external devices.
EOS User's manual
Daeumling & Zimmermann
Page 9
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