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IBM 7090 User Manual

IBM 7090
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The
circuits
in
the
multiplexor
are
actually
switching
circuits
rather
than
registers.
These
switching
functions
allow
either
the
CPU
or
the
data
channel
to
use
storage
for
purposes
of
addressing
and
data
transmission.
The
multiplexor
also
signals
storage
whether
the
operation
is
to
be
stored
or
read
out,
governed
by
control
from
the
CPU
or
data
channel.
The
storage
register
accepts
a
word
from
storage
for
use
by
the
CPU,
or
from
the
CPU
for
forwarding
to
the
memory
data
register.
This
is
true
for
both
instructions
and
data.
The
storage
register
also
plays
a
part
in
certain
arithmetic
and
logic
opera-
tions
that
are
not
used
in
A+B =
C,
print
C.
The
address
register
and
program
counter
are
the
addressing
registers
of
the
CPU.
The
address
register,
in
every
CPU
operation
involving
storage,
contains
the
storage
address.
This
address
is
sent
to
the
memory
address
register
when
CPU
is
using
stor-
age.
The
program
counter
keeps
account
of
the
progress
of
the
program.
This
counter
normally
advances
by
one
after
each
instruction
has
been
called
for.
Thus,
the
normal
course
of
events
is
to
call
for
instructions
from
ascending
addresses
in
storage.
When
one
operation
is
complete,
the
current
reading
in
the
program
counter
goes
to
the
ad-
dress
register
for
forwarding
to
the
memory
address
register.
The
author
of
the
pro-
gram
is
responsible
for
having
the
next
instruction
stored
at
this
address.
The
adders
and
accumulator
are
the
main
arithmetic
components
of
the
entire
sys-
tem.
Although
the
adders
are
not
registers
and
have
no
capacity
for
holding
numbers,
they
play
such
a
prominent
part
in
almost
every
CPU
operation
that
they
cannot
be
con-
sidered
as
an
ordinary
switching
circuit.
The
adders
perform
a
merging
function,
having
the
capacity
for
operating
on
an
entire
word
at
one
time.
Numbers
from
two
sources
can
be
added
together
and
carries
simultaneously
added
in.
Two
full
words
can
be
sent
to
the
adders,
and
the
complete
answer
can
be
taken
almost
immediately
to
a
register.
In
addition,
the
adders
provide
the
only
means
of
entry
to
the
accumulator
and
the
only
direct
route
from
the
address
field
of
the
storage
register
to
the
address
register.
The
major
use
of
the
accumulator
is
to
receive
the
output
of
the
adders.
The
name
accumulator,
although
not
completely
appropriate
for
a
noncounting,
nonadding
register,
is
applicable
in
that
this
register
receives
and
holds
sums
from
the
adders.
The
program
register
receives
and
holds
the
operation
code
of
each
CPU
instruction.
Decoding
the
configuration
of
binary
bits
in
the
positions
of
this
register
establishes
the
controls
for
the
operation
to
be
done.
Each
time
that
an
operation
is
ended
and
a
new
one
is
to
begin,
the
old
operation
code
is
cleared
from
the
program
register
and
the
new
code
is
set
in.
Thus,
the
controls
for
the
operation
completed
are
dropped
and
the
controls
for
the
new
operation
are
brought
into
effect.
2.4.00
A+B =
C,
PRINT
C
The
following
explanation
of
7090
's
operation
in
performing
A+B =
C,
print
C
is
more
detailed
than
the
general
sequence
in
Section
1.
4.1.
Review
that
section
before
proceeding.
17

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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