Basic
Compute
The basic 503 forms a powerful and complete
computing system in its own right; it has amagnetic
core store of 8192 words capacity
with
a cycle-time
of 3.5 microseconds. Each word in the store may be
regarded as equivalent to
(a) a fixed point number of 39 binary digits,
equivalent to
11
decimal digits
(b) a floating-point number using nine binary
digits
for the exponent and 30 for the mantissa,
corresponding to a precision of nine decimal digits
(c) Five alphanumeric characters, or
(d) Two single-address instructions.
Input and output for the basic computer is on
punched paper tape, read at
1000
characters per
second and punched at one hundred characters per
second. There are two tape readers and two tape
punches. Eight-channel paper tape is normally used
on the 503, but the equipment can also handle five-
channel paper tape.
The computer
is
controlled from an electric type-
writer which is used for direct input and output.
The basic pulse rate of the 503 is
6.7
megacycles
per second.
The computercontains a parallelbinary arithmetic
unit, and
is
capable of carrying out 100,000 opera-
tions every second.
Typical operation times,inclusiveof store access,
are
as
follows
Fixed-point addition
7
microseconds
Floating-point addition average
20
microseconds
Transfer control
5
microseconds
Fixed-point multiplication
38
to
57
microseconds
Floating-point multiplication
38
to
51
microseconds
Fixed-point division
8
I
microseconds
Floating-point division
7
I
microseconds
The time for the inner loop of matrix multiplica-
tion routine is
126
microseconds, so that two 50 by
50
matricescan be multiplied together
in
16
seconds.
The timerequired to sort ~o,oooitemsof
10
words
each on a 503 with four magnetic tape decks is
estimated at
4
minutes.
Information may be transferred directly between
peripheraldevicesand any block ofconsecutiveloca-
tions in the
main
store of the computer. Once the
transferhas been starteditproceeds under the control
of the Peripheral Control Unit whilst the computer
continues
with
its programme. "Tagw bits
associated with each word in the store of the
computer are used to ensure that the computer
cannot refer to the block of store involved
in
a
transfer untilthenew information has arrived,orthe
old information has been used. However, the com-
puter can refer to the earlier locations of the block
whilst the later locations are still involved
in
the
transfer. These arrangementsare entirely automatic
and need not concernthe programmerwhen writing
his programme.
