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Another exception to valid program-
ming is addressing a byte location that
is not available on your particular
model of System/360.
The largest size
main storage that is available on the
Model 30 is 65,536 bytes.
Any address
other than 00000-65535 results in a
program check.
This type of check is
known as an addressing exception.
Central Processing Unit (CPU)
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The two main sections of the CPU are
(1) the control section and (2) the
arithmetic and logical unit (ALU).
The CPU uses variable field length
instructions for storage to storage
operations.
Variable fields can be up to 256
bytes long.
The CPU uses fixed length instruc-
tors for storage to register or
register to register operations.
Fixed length fields can be
half-word, word, or double-word
fields.
Register-to-register or storage to
register operations use any of 16
general purpose registers.
Floating point operations use any of
4 double-word floating-point reg-
isters
In Figure 1-10, you can see the logical
1-12
structure of the CPU for the System/360
and its relationship to the main
storage.
There are two main sections in CPU.
They are (1) the control section and (2)
the arithmetic and logical unit (ALU).
From Figure 1-10, you should be able
to see some of the functions of the
control section.
They are:
1.
All references to main storage,
whether for instructions or for
data, are made by the control sec-
tion.
2.
During the first part of any
instruction, the control section
addresses main storage and causes
the instruction to be fetched and
sent to the control section.
The
instruction is then decoded by the
control section and executed during
the latter part.
The ALU contains the circuits neces-
sary for adding and comparing data
fields as well as the other circuits
necessary for operating on data fields.
As can be seen from Figure 1-10, the
ALU can do:
1.
Variable field length operations.
2.
Fixed-point operations involving
fixed-length fields.
3.
Floating point operations.
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