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Register-to-Register:
With sixteen
general registers, sometimes both fixed
length binary operands will be in gener-
al registers.
In these cases, another
data flow concept is used
(register-to-register operation, Figure
1-17) •
Addresses
Contral
Section
Instruction
Main
Storage
Fixed
length
I
I
AlU
General
Registers
0-15
Figure 1-17.
System/360 Register to
Register Operations
Floating-Point Operation:
Floating
point is the term given to arithmetic
operations involving a fraction and an
exponent.
For instance:
217,000 can be expressed as:
.217
x 10·
296,000 can be expressed as:
.296
x 10.
Fixed point arithmetic would add the
numbers thusly:
1-16
217,000
+ 296,000
513,000
I
Floating point arithmetic would do it
like this:
.217 x 10·
+ .296
x
10.
.513
X
10
6
Floating-point arithemetic is most
useful for expressing very large numbers
and operating on them with much
precision.
To do floating point arith-
metic the System/360 has four floating
point
re~isters
(Figure 1-18).
Addresses
Main
I
Storage
Control
Instructions
I
Section
•
I
Floating
AlU
Point
1 1
Four floating Point
Registers
Figure 1-18.
Floating Point
Registers
The four floating point registers are
numbered 0, 2, 4, 6.
These are not the
same as general registers 0, 2,
4, 6.
The floating point registers are separ-
ate registers used only as accumulators
during floating point operations.
The floating point registers are
double word registers and are addressed
by a four bit binary address in floating
point instructions.
Bits 0
63
r------------------,
I
F~P.
Reg 6
I
L-_________________
J
F.P. Reg Address
=
0110
Logical vs Hardware Structure of
System/360:
The structure of the
System/360 which you have been learning
is its logical structure: By this we
mean that this is the way the System/360
appears to the programmer.
The manner
in which this logical structure is
implemented will vary between the dif-
ferent models of the System/360.
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