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IBM 7090 User Manual

IBM 7090
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Carry
From
Adder
9
to
Adder
8
A
special
circuit
can
prevent
or
allow
a
carry
from
adder
9
to
adder
8.
The
reason
for
this
is
that
a
floating-point
word
has
two
separate
parts,
a
characteristic
(positions
1-8)
and
a
fraction
(positions
9-35).
During
some
floating-point
operations,
a
carry
out
of
the
fraction
must
not
be
allowed
to
gate
to
the
characteristic.
3.2.00
INSTRUCTION DECODING AND
PROCESSING
The
output
of
the
program
counter
is
gated
to
the
address
register
through
the
address
switches.
The
output
of
the
address
register
is
then
used
to
locate
the
address
of
the
instruction
in
core
storage.
The
output
of
core
storage
is
sent
to
the
storage
register
and
the
operation
code
is
also
sent
to
the
program
register.
The
output
of
the
program
register
then
is
decoded
to
instruct
the
system.
3. 2.
01
Operation
Decoders
The
output
of
the
program
register
feeds
two
decoders.
The
outputs
of
positions
1-5
feed
the
primary
operation
decoders
(POD), and
the
outputs
of
positions
6-9
feed
the
secondary
operation
decoders
(SOD).
The
primary
operation
is
used
to
establish
the
basic
execution
control
routing.
The
secondary
operation
decoder
is
used
only
for
the
sense,
or
primary
operation
76
instructions.
Some
similar
instructions
have
the
same
primary
operation
code.
Direct
outputs
of
the
program
register
or
storage
register
are
sent
to
individual
machine
circuits
to
cause
the
machine
to
operate
according
to
the
minor
differences
among
these
similar
instructions.
3.
2. 02
Control
Circuits
The
control
circuits
cause
the
machine
to
operate
according
to
the
decoding
of
the
instruction.
Specific
control
circuits
cause
data
to
be
moved
and
functions
to
be
per-
formed
so
the
machine
gives
the
desired
results
of
the
instruction.
3.
2. 03
Pulses
The
control
circuits
require
a
great
number
of
pulses
and
gates.
These
pulses
and
gates,
obtained
by
mixing
clock
pulses
from
the
multiplexor
clock,
function
in
the
7090
as
the
circuit
breakers
function
in
electro-mechanical
card
machines.
They
are
used
to
establish
proper
sequence
of
operation
in
the
system.
3.3.00
BASIC
CYCLE
The
basic
cycle
in
the
CPU
is
2.1818
microseconds.
It
is
divided
into
12
equal
times
of
the
181.
8
milli-microseconds
each.
The
12
times
,are
sent
to
the
CPU
from
the
multiplexor.
There
are
three
different
types
of
cycles
used
by
the
CPU.
These
are:
1.
Instruction
I
cycle
2.
Execution
E
cycle
3.
Logic
L
cycle
Every
instruction
has
an
I
cycle.
This
cycle
brings
the
instruction
from
core
stor-
age
to
the
CPU,
where
the
instruction
is
decoded.
Some
instructions
require
only
the
I
cycle
for
their
execution;
most
instructions
require
additional
cycles.
36

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IBM 7090 Specifications

General IconGeneral
CategoryMainframe Computer
Introduced1959
Transistor-basedYes
Word Length36 bits
Add Time4.8 microseconds
MemoryCore memory
Memory (words)32, 768 words