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IBM 7090 User Manual

IBM 7090
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when
one
operation
is
about
finished
and
an
instruction
is
needed.
The
author
of
the
program
must
provide
the
proper
instruction
word
in
storage
and
must
build
his
program
so
that
the
CPU
has
the
address
for
that
instruction
when
it
is
needed.
Each
field
of
the
instruction
word
has
its
particular
significance
because
the
CPU
brings
the
word
in
as
an
instruction.
The
sign
position
is
always
a
part
of
the
operation
code.
Along
with
the
sign,
either
the
remainer
of
the
prefix
field
or
the
decrement
field
dictates
what
operation
is
to
be
done.
If
there
is
nothing
in
the
remainder
of
the
prefix,
the
sign
and
decrement
contain
the
operation
code.
If
either
of
the
two
remaining
posi-
tions
of
the
prefix
contains
a
bit,
the
prefix
contains
the
entire
operation
code
and
the
decrement
field
is
used
for
another
purpose.
The
address
field
usually
contains
the
address
of
a
data
word
in
storage.
This
data
word
is
brought
into
the
CPU
as
a
part
of
whatever
arithmetic
or
logic
function
is
called
for
by
the
operation
code.
Thus,
the
instruction
not
only
dictates
the
operation
to
be
performed,
but
also
specifies
the
address
of
the
data
to
be
used.
In
some
instances,
the
address
field
is
a
part
of
the
operation
code.
When
this
is
the
case,
the
address
field
is
not
used
to
address
data
in
storage.
The
tag
field
is
a
means
of
causing
the
CPU
to
calculate
a
storage
address
that
is
different
from
the
address
field
of
the
instruction.
2.2.03
Data
Channel
Command
Word
Similar
in
format
and
application
to
the
CPU
instruction
word,
the
data
channel
com-
mand
word
gains
its
special
significance
by
being
called
out
of
storage
by
the
control
function
in
the
data
channel.
This,
as
in
CPU,
occurs
when
one
operation
is
finished
and
the
data
channel
needs
to
be
directed
what
to
do
next.
The
two
major
differences
are
that:
1.
The
prefix
is
always
the
operation
code
in
the
data
channel.
2.
Positions
3-17
are
a
word
counter.
Whether
the
operation
is
reading
or
writing,
once
the
command
is
in
channel,
the
word
count
becomes
one
less
each
time
a
word
is
handled.
Thus,
when
the
word
count
becomes
zero,
the
channel
must
ask
for
a
new
command.
Data
channel
operations
always
start
by
unit
selection
from
a
CPU
instruction.
Independent
operation
continues
on
the
same
unit
as
long
as
successive
commands
re-
quire
it.
Once
the
succession
of
commands
is
broken
by
a
command
to
disconnect,
that
unit
and
the
channel
that
was
operating
have
completed
their
assignment.
This
is
all
planned
in
advance
by
the
author
of
the
program,
and
commands
are
stored
where
the
data
channel
will
call
for
them
at
the
proper
time.
2.3.00
FUNDAMENTAL
COMPONENTS
-The
fundamental
components
described
in
this
section
are
the
operating
features
(Figure
2.3-1)
used
in
the
operation
A+B =
C,
print
C.
For
the
most
part,
these
are
groups
of
binary
storage
positions
where
information
may
be
placed
outside
of
the
stor-
age
unit
itself.
These
groups
are
commonly
called
registers.
14

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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