I
I
V
REGISTERS
Eight V
registers,
each
with
64
elements are the major computational
registers
of the
CRAY-l.
Each
element of a V
register
has
64
bits.
When
associated data
is
grouped
into successive elements of a V
register,
the
register
quantity
may
be
considered a vector.
Examples
of vector
quantities
are
rows
or
columns
of a matrix or elements of a
table.
Computational efficiency
is
achieved
by
processing
each
element of a
vector
identically.
Vector
instructions
provide for the
iterative
processing of successive vector
register
elements. A vector operation
begins
by
obtaining operands
from
the
first
element of
one
or
more
V
registers
and
delivering the
result
to the
first
element of a V
register.
Successive elements are provided
each
clock period
and
as
each
operation
is
performed, the
result
is
delivered to successive elements of the
result
V
register.
The
vector operation continues until the
number
of
operations performed
by
the
instruction
equals a count specified
by
the
contents of the vector length
(VL)
register.
Vectors having lengths
exceeding
64
are handled under
program
control in groups of
64
and
a
remainder.
A
result
may
be
received
by
a V
register
and
retransmitted
as
an
operand
to a subsequent operation in the
same
clock period. This
use
of a
register
as
both a
result
and
operand
register
allows for the "chaining" of
two
or
more
vector operations together.
In
this
mode,
two
or
more
results
may
be
produced per clock period.
The
contents of a V
register
are transferred to or
from
memory
in a block
mode
by
specifying a
first
word
address in
memory,
a positive or negative
increment for
computing
memory
addresses,
and
a vector length.
The
trans-
fer
then proceeds beginning with the
first
element of the V
register
at
a
maximum
rate
of
one
word
per clock period, depending
on
bank
conflicts.
Single-word data
transfers
are possible
between
an
S
register
and
an
element
of a V
register.
In
this
manual, the V
registers
are individually referred to
by
the
letter
V
and
a
numeric
suffix
in the range 0 through
7.
Vector
instructions
reference V
registers
by
allowing
specification
of the
suffix
as
the
i,
j,
or k designator as described in section 4 of
this
manual.
2240004
3-4
E
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