RELIABILITY—NO WRONG RESULTS:
BELL LABORATORIES’ GENERAL-PURPOSE RELAY CALCULATOR
In 1946, Bell Telephone Laboratories in New York finished two
_general-purpose relay calculators_—mechanical brains. They were twins.
One was shipped in July 1946 to the National Advisory Committee for
Aeronautics at Langley Field, Virginia. The other, after some months of
trial operation, was shipped in February 1947 to the Ballistic Research
Laboratories at the U. S. Army’s Proving Ground, Aberdeen, Md.
Each machine is remarkably reliable and versatile. It can do a wide
variety of calculations in a great many different ways. Yet the machine
never takes a new step without a check that the old step was correctly
performed. There is, therefore, a chance of better than 99.999,999,999
per cent that the machine will not let a wrong result come out. The
automatic checking, of course, does not prevent (1) human mistakes—for
example, instructing the machine incorrectly—or (2) mechanical
failures, in which the machine stops dead in its tracks, letting no
result at all come out.
ORIGIN AND DEVELOPMENT
In Bell Telephone Laboratories the telephone system of the country is
continually studied. Their research produced the common type of dial
telephone system: a masterly machine for selecting information.
Now when a telephone engineer studies an electric circuit, he often
finds it very convenient to use numbers in pairs: like 2, 5 or-4,-1.
Here the comma is a separation sign to keep the two numbers in the pair
separate and in sequence. Mathematicians call numbers of this kind, for
no very good reason, _complex numbers_; of course, they are far less
complex than why the sun shines or why plants grow.
When Bell Laboratories test the design of new circuits, girl computers
do arithmetic with complex numbers. Addition and subtraction are
easy: each means two operations of addition or subtraction of
ordinary numbers. For example, 2, 5, plus-4,-1 equals 2-4, 5-1, which
equals-2, 4. And 2, 5 minus-4,-1 is the same as 2, 5 plus 4, 1; and
this equals 2 + 4, 5 + 1, which equals 6, 6. Multiplication of two
complex numbers, however, is more work. If _a_, _b_ and _c_, _d_ are
two complex numbers, then the formula for their product is (_a_ ×
_c_)-(_b_ × _d_), (_a_ × _d_) + (_b_ × _c_). To get the answer, we
need 4 multiplications, 1 subtraction, and 1 addition. Division of two
complex numbers requires even more work. If _a_, _b_ and _c_, _d_ are
two complex numbers, the formula for the quotient of _a_, _b_ divided
by _c_, _d_ is:
[(_a_ × _c_) + (_b_ × _d_)] ÷ [(_c_ × _c_) + (_d_ × _d_)],
[(_b_ × _c_) - (_a_ × _d_)] ÷ [(_c_ × _c_) + (_d_ × _d_)]
For example,
(2, 5) ÷ (-4, -1) = [(2 × -4 = -8) + (5 × -1 = -5)]
÷ [(-4 × -4 = 16) + (-1 × -1 = 1)],
[(5 × -4 = -20) - (2 × -1 = -2)] ÷ [16 + 1] = -(¹³/₁₇), -(¹⁸/₁₇)
Thus, division of one complex number by another needs 6
multiplications, 2 additions, 1 subtraction, and 2 divisions of
ordinary numbers—and always in the same pattern or sequence.
The Complex Computer
About 1939, an engineer at Bell Telephone Laboratories in New York, Dr.
George R. Stibitz, noticed the great volume of this pattern arithmetic.
He began to wonder why telephone switching equipment could not be used
to do the multiplications and divisions automatically. He decided it
could. All that was necessary was that the _relays_ (see Chapter 2)
used in regular telephone equipment should have a way of remembering
and calculating with numbers. Regular telephone equipment would take
care of the proper sequence of operations. Regular equipment known as
_teletypewriters_ would print the numbers of the answer when it was
obtained. A teletypewriter consists essentially of a typewriter that
may be operated by electrical impulses. It has a keyboard that may
produce electrical impulses in sets corresponding to letters; and it
can receive or transmit over wires.
Dr. Stibitz _coded_ the numbers: each decimal digit was matched up with
a group of four relays in sequence, and each of these relays could be
open or closed. If 0 means open and 1 means closed, here is the pattern
or code that he used:
DECIMAL DIGIT RELAY CODE
0 0 0 1 1
1 0 1 0 0
2 0 1 0 1
3 0 1 1 0
4 0 1 1 1
5 1 0 0 0
6 1 0 0 1
7 1 0 1 0
8 1 0 1 1
9 1 1 0 0
With regular telephone relays and regular telephone company techniques,
Dr. Stibitz and Bell Telephone Laboratories designed and constructed
the machine. It was called the _Complex Computer_ and was built just
for multiplying and dividing complex numbers. Six or eight panels of
relays and wires were in one room. Two floors away, some of the girl
computers sat in another room, where one of the teletypewriters of
the machine was located. When they wished, they could type into the
machine’s teletypewriter the numbers to be multiplied or divided. In a
few seconds back would come the answer. In fact, there were two more
computing rooms where teletypewriters of the machine were stationed. To
prevent conflicts between stations, the machine had a circuit like the
busy signal from a telephone.
In 1940, a demonstration of the Complex Computer took place: the
computing panels remained in New York, but the teletypewriter
input-output station was set up at Dartmouth College in Hanover, N. H.
Mathematicians gave problems to the machine in Dartmouth, it solved
them in New York, and it reported the answers in Dartmouth.
Special-Purpose Computers
With this as a beginning, Bell Laboratories developed another machine
for a wide variety of mathematical processes called _interpolating_
(see Supplement 2). Then, during World War II, Bell Laboratories made
more special-purpose computing machines. They were used in military
laboratories charged with testing the accuracy of instruments for
controlling the fire of guns. These computers took in a set of
gun-aiming directions put out by the _fire-control instrument_ in
some test. They also took in the set of observations that went into
the fire-control instrument on that test. Then they computed the
differences between the gun-aiming produced by the fire-control
instrument and the gun-aiming really required by the observations.
Using these differences, the fire-control instrument could be adjusted
and corrected. These special-purpose computers were also useful in
checking the design of new fire-control instruments and in checking
changes due to new types of guns or explosives.
Regularly, after each of these special-purpose computers was finished,
people began to put other problems on it. It seemed to be fated that,
as soon as you had made a machine for one purpose, you wanted to use
it for something else. Accordingly, in 1944, two agencies of the U. S.
Government together made a contract with Bell Telephone Laboratories
for two general-purpose relay computers. These two machines were
finished in 1946 and are twins.
ORGANIZATION OF THE GENERAL-PURPOSE COMPUTER
When a man sits down at a desk to work on a computation, he has six
things on his desk to work with: a work sheet; a desk calculator, to
add, subtract, multiply, and divide; some rules to be followed; the
tables of numbers he will need; the data for the problem; and an answer
sheet. In his head, he has the capacity to make decisions and to do
his work in a certain sequence of steps. These seven subdivisions of
calculation are all found in the Bell Laboratories’ general-purpose
relay computer. The general-purpose computer is a computing system, in
fact, more than it is a single machine. The part of the system which
does the actual calculating is called, in the following paragraphs,
the _computer_, or else, since it is in two halves, _Computer 1_ and
_Computer 2_.
Physical Units
The computing system delivered to the Ballistic Research Laboratories
fills a room about 30 by 40 feet and consists of the following:
2 _computers_: panels of relays, wiring, etc.,
which add, subtract, multiply, divide, select,
decide, control, etc.
4 _problem positions_: tables each holding 12
mechanisms for feeding paper tape, which read numbers
and instructions punched on tape and convert them
into electrical impulses.
2 _hand perforators_: keyboard devices for
punching instructions and numbers on paper tape.
1 _processor_: a table holding mechanisms for
feeding 2 paper tapes and punching a third paper
tape, used for checking numbers and instructions
punched on tape.
2 _recorders_: each a table holding a
teletypewriter, a tape punch, and a tape feed, used
for recording answers and, if necessary, consulting
them again.
The 2 computers correspond to the work sheet, the desk calculator,
and the man’s capacity to make decisions and to carry out a sequence
of steps. The 4 problem positions correspond to the problem data, the
rules, and the tables of numbers. The 2 recorders correspond to the
answer sheet. The 2 hand perforators and the processor are auxiliary
machines: they translate the ordinary language of arithmetic into the
machine language of punched holes in paper tape.
This is the computing system as organized for the Ballistic Research
Laboratories at Aberdeen. The one for the National Advisory Committee
for Aeronautics has only 3 problem positions. The computer system may,
in fact, be organized with 1 to 10 computers and with 1 to 20 problem
positions.
The great bulk of this computing system, like the mechanical brains
described in previous chapters, is made up of large numbers of
identical parts of only a few kinds. These are: standard telephone
relays; wire; and standard _teletype transmitters_, mechanisms that
read punched paper tape and produce electrical impulses.
Numbers
The numbers that the Bell machine contains range from 0.1000000 to
0.9999999 times a _power_ of 10 varying from 10,000,000,000,000,000,000
to 0.000,000,000,000,000,000,1, or, in other words, from 10¹⁹ to 10⁻¹⁹.
The machine also contains zero and _infinity_: zero arises when the
number is smaller than 10⁻¹⁹, and infinity arises when the number is
equal to or greater than 9,999,999,000,000,000,000. (See Supplement 2.)
The system used in the machine to represent numbers on relays is called
_biquinary_—the _bi_-, because it is partly twofold like the hands, and
the -_quinary_ because it is partly fivefold like the fingers. This
system is used in the abacus (see Chapter 2 and Supplement 2). In the
machine, for each decimal digit, 7 relays are used. These relays are
called the 00 and 5 relays, and the 0, 1, 2, 3, and 4 relays. If, as
before, 0 indicates a relay that is not energized and 1 indicates a
relay that is energized, then each decimal digit is represented by the
positioning of the 7 relays as follows:
DECIMAL DIGIT RELAYS
00 5 0 1 2 3 4
0 1 0 1 0 0 0 0
1 1 0 0 1 0 0 0
2 1 0 0 0 1 0 0
3 1 0 0 0 0 1 0
4 1 0 0 0 0 0 1
5 0 1 1 0 0 0 0
6 0 1 0 1 0 0 0
7 0 1 0 0 1 0 0
8 0 1 0 0 0 1 0
9 0 1 0 0 0 0 1
Then, for any decimal digit, one and only one of the 00 and 5 relays
is energized, and one and only one of the 0, 1, 2, 3, and 4 relays
is energized. If more or less than exactly one relay in each set is
energized, then the machine knows that it has made a mistake, and it
stops dead in its tracks. Thus any accidental failure of a relay is at
once caught, and the chance of two compensating failures occurring at
the same time is extremely small.
HOW INFORMATION GOES INTO THE MACHINE
In order to put a problem into this machine—just as with the other
machines—first a mathematician who knows how the problem is to be
solved, and who knows how to organize it for the machine, lays out
the scheme of calculation. Then, a girl goes to one of the hand
perforators. Sitting at the keyboard, she presses keys and punches out
feet or yards of paper tape expressing the instructions and numbers
for the calculation. Each character punched—digit, letter, or sign—has
one or more of a maximum of 6 holes across the tape. Another girl,
using the other hand perforator, also punches out the instructions and
numbers for the calculation. If she wishes to erase a wrong character,
she can press an _erase key_ that punches all 6 holes, and then the
machine will pass by this row as if it were not there.
Three kinds of tapes are produced for the machine:
_Problem tapes_, which contain information
belonging to the particular problem.
_Table tapes_, which contain tables of numbers to
be referred to from time to time.
_Routine tapes_, which contain the program, or
routine, or sequence of steps that the machine is to
carry out.
In each of these tapes one character takes up ⅒ of an inch along the
tape. In the case of a table tape, however, an ordinary 1-digit number
requires 4 characters on the tape, and a 7-digit number requires 11
characters on the tape. On a table tape there will be on the average
about 1 inch of tape per number.
The Processor
The two paper tapes prepared on the perforator should agree. But
whether or not they agree, a girl takes them over to the processor and
puts them both in. The processor has two tape feeds, and she puts one
tape on each and starts the machine. The processor compares them row by
row, making sure that they agree, and punches a new tape row by row.
If the two input tapes disagree, the processor stops. You can look to
see which tape is right, and then you can put the correct punch into
the new tape with a keyboard mounted on the processor. As the processor
compares the two input tapes, it also converts any number written in
the usual way into machine language. For example, the processor will
automatically translate 23,188 into +.231 8800 × 10⁺⁵. The processor
also puts in certain safeguards. If you want it to, the processor will
also make a printed record of a tape. Also, when a tape becomes worn
from use in the machine, you can put it into the processor and make a
fresh copy.
The Problem Positions
Next, the girl takes the punched tape made by the processor over to a
problem position that is idle. Two of the problem positions are always
busy guiding the two computers. The other two problem positions stand
by, ready to be loaded with problems.
A problem position looks like a large covered-over table. Under
the covers are 12 tape feeds, or _tape transmitters_. All these
transmitters look exactly alike except for their labels and consist
of regular teletype transmitters. Six-hole paper tape can be fed into
any transmitter. Six metal fingers sense the holes in the paper tape
and give out electrical impulses at proper times. At the front of the
problem position is a small group of switches that provide complete
control over the problem while it is on the machine. These are switches
for starting, disconnecting, momentary stop, etc.
One tape transmitter is the problem tape transmitter. It takes in
all the data for the problem such as the starting numbers. The first
thing it does at the start of a problem is to check (by comparing tape
numbers) that the right tapes are in the right feeds.
Five transmitters are routine tape transmitters. Each of these takes
in the sequence of computing steps. The routine tapes also contain
information for referring to table tapes and instructions for printing
and punching tape. The machine can choose according to instructions
between the five routine tapes and can choose between many different
sections on each tape. Therefore, we can use a large number of
different routines in a calculation, and this capacity makes the
machine versatile and powerful.
Six transmitters are table tape transmitters. They read tables of
numbers when directed to. A table tape can be as long as 100 feet and
will hold numbers at the rate of 1 inch per number, so that about 1200
numbers of seven decimal digits can be stored on a table tape.
When we look up a number in a table, such as the following,
2½ 3 3½ ···
+————————————————————————————
1 |1.02500 1.03000 1.03500
2 |1.05063 1.06090 1.07123
3 |1.07689 1.09273 ···
4 |1.10381 ··· ···
5 |1.13141 ···
6 |1.15969
7 | ···
8 | ···
9 | ···
10 |
···| ···
we look along the top and down the side until we find the column and
row of the number we are looking for. These are called the _arguments_
of the _tabular value_ that we are looking for (see Supplement 2).
Now when we put this table on a tape to go into the Bell Laboratories
machine, we write it all on one line, one figure after another, and we
punch it as follows:
2-½ 1-5 1.02500 1.05063 1.07689 1.10381 1.13141
6-10 1.15969 ··· 11-15 ··· ··· ··· 3
1-5 1.03000 1.06090 ··· ··· 3½ 1-5 1.03500
···
You will notice that the column labels 2½, 3, 3½ have been put on the
tape, each in front of the group of numbers they apply to. The row
labels 1 to 5, 6 to 10, ··· have also been put on the tape, each in
front of the group of numbers they apply to. The appropriate column
and row numbers, or arguments, must be put often on every table tape,
so that it is easy for the machine to tell what part of the table tape
it is reading.
In the Bell Laboratories machine, we do not need to put equal _blocks_
of arguments like 1-5, 6-10 ··· on the table tape. Instead we can put
individual arguments like 1, 2, 3, 4 ···, or, if we wish, we can use
blocks of different sizes, like 1-3, 4-15, 16-30···. For some tables,
such as income tax tables, it is very useful to have varying-sized
blocks of arguments. The machine, when hunting for a certain value in
the table, makes a comparison at each block of arguments.
The machine needs about 6 seconds to search a foot of tape. If we want
to set up a table economically, therefore, we need to consider the
average length of time needed for searching.
[Illustration: FIG. 1. Scheme of a recorder.]
HOW INFORMATION COMES OUT OF THE MACHINE
At either one of the two recorders (Fig. 1), information comes out of
the machine, either in the form of printed characters or as punched
tape. The recorder consists of a _printer_, a _reperforator_, and
a tape transmitter. One recorder table belongs to each computer
and records the results it computes. The printer is a regular
teletypewriter connected to the machine. It translates information
produced by the machine as electrical impulses and prints the
information in letters and digits on paper. The reperforator is an
automatic tape punch. It translates information produced by the machine
in the form of electrical impulses and punches the information on
paper tape. Next to the tape punch is a tape transmitter. After the
tape comes through the punch, it is fed into the transmitter. Here the
machine can hunt for a previous result punched in the tape, read that
result, and use it again.
HOW INFORMATION IS MANIPULATED IN THE MACHINE
The main part of the computing system consists of 27 large frames
loaded with relays and wiring, called the _computer_, or _Computer 1_
and _Computer 2_. In this “telephone central station,” all the “phone
calls” from one number to another are attended to. There are 8 types of
these frames in the computer:
FRAMES NUMBER
Storing register frames 6
Printer frames 2
Problem frames 2
Position frames 2
Calculator frames 6
Control frames 2
Routine frames 4
BTL (Block-Trig-Log) frames 2
Permanent table frames 1
——
Total 27
In most but not quite all respects, the two halves, _Computer 1_ and
_Computer 2_, can compute independently. The _storing register frames_
hold enough relays to store 30 numbers. The registers for these
numbers are named _A, B, C, D_, ···, _M, N, O_ in two groups of 15
each. One group belongs to Computer 1 and the other to Computer 2. In
each Computer, the _calculator frames_ hold enough relays for storing
two numbers (held in the _X_ and _Y_ registers) and for performing
addition, subtraction, multiplication, division, and square root. In
each Computer, the _problem frame_ stores the numbers that are read off
the problem tape and the table tapes, and the _printer frame_ stores
the numbers that are read into the printer. The printer frame also
stores indications, for example, the signs of numbers, plus or minus,
for purposes of combining them. These frames also hold the relays that
control the printer, the problem tape, and the table tapes. Jointly for
both Computers, the _position frames_ connect a problem in some problem
position to a Computer that becomes idle. For example, one problem
may finish in the middle of the night; the machine automatically and
unattended switches to another problem position and proceeds with the
instructions there contained. A backlog of computing on hand can be
stored in two of the problem positions, while the other two control the
two Computers. In each Computer, the _routine frames_ hold the relays
that make the Computer follow the routine instructions. Jointly for
both Computers, the remaining frames—the _control frames_, the _BTL
frames_, and the _permanent table frames_—hold the relays that control:
the alarms and lights for indicating failures; some circuits called the
BTL controls; the tape processor; and the mathematical tables that are
permanently wired into the machine. The permanent table frames hold the
following mathematical functions (see Supplement 2): _sine_, _cosine_,
_antitangent_, _logarithm_, and _antilogarithm_.
Storing
Numbers can be stored in the machine in the 30 regular storing
registers of both Computers together. They can also be stored, at the
cost of tying up some machine capacity, in the other registers: the 4
calculator registers, the 2 problem registers, the 2 table registers,
and the 2 printer registers. Numbers can also be punched out on tape,
in either of the two printers, and later read again from the tape.
Labels identifying the numbers can also be punched and read again from
the tape.
Each register in the machine stores a number in the biquinary notation,
as explained above. In programming the machine, after mentioning a
register it is necessary—as a part of the scheme for checking—to tell
the machine specifically whether to hold the number in the register or
to clear it.
Addition and Subtraction
The calculator frames can add two numbers together, if so instructed in
the routine tape. Suppose that the two numbers are in the registers
_B_ and _D_ and that we wish to put the sum in register _F_. Suppose
that we wish to clear the _D_ number but hold the _B_ number after
using them. The code on the routine tape is _B H_ + _D C_ = _F_. _H_
and _C_ coming right after the names of the registers always designate
“hold” and “clear,” respectively.
The calculator frames can, likewise, subtract a number. The routine
instruction _B H_-_D C_ = _F_ means:
Take the number in register _B_ (hold it); subtract the
number in _D_ (clear it); put the result in _F_
Multiplication and Division
The calculator frames perform multiplication by storing the digits of
the multiplier, adding the multiplicand over and over, and shifting,
until the product is obtained. However, if the multiplier is 1989, for
example, the calculator treats it as 2000-11. This short-cut applies
to digits 6, 7, 8, 9 and cuts the time required for multiplying. The
routine instruction is _B H_ × _D C_ = _F_.
The calculator performs division by repeated subtraction. The routine
instruction is _B H_ ÷ _D C_ = _F_. The operation signs +,-, ×, ÷
actually appear on the keyboard of the perforator and on the printed
tape produced by the printer.
Discrimination
_Discrimination_ is the term used in the Bell Laboratories computer for
what we have previously called selection, or comparison, or sequencing.
The _discriminator_ is a part of the calculator that compares or
selects or decides—“discriminates.” The discriminator can decide
whether a number is zero or not zero. In the language of the _algebra
of logic_ (see Chapter 9 and Supplement 2), if _a_ is a number, the
discriminator can find _T_(_a_ = 0). The discriminator can also decide
whether a number is positive or negative. In the language of logic, it
can find _T_(_a_ > 0) or _T_(_a_ < 0). The actions that a discriminator
can cause to be taken are:
Stop the machine.
Stop the problem, and proceed to another problem.
Stop the routine going on, and proceed with a new routine.
Permit printing, or prevent printing; etc.
In this way the discriminator can:
Distinguish between right and wrong results.
Tell that a certain result is impossible.
Recognize a certain result to be the answer.
Control the number of repetitions of a formula.
Change from one formula to another formula.
Check a number against a tolerance; etc.
PROBLEMS
Among the problems that have been placed on the machine successfully
are: solving the _differential equation_ of a _trajectory_ (see Chapter
5) and solving 32 _linear simultaneous equations_ in 32 _unknowns_ (see
Supplement 2). In the second case, the routine tapes were designed to
apply equally well to 11 to 100 linear equations in 11 to 100 unknowns.
However, the machine can do a very broad class of problems, including,
for example, computing a personal income tax. This calculation with all
its complexity of choices cannot be placed on any of the mechanical
brains described in previous chapters. The machine can, of course, be
used to calculate any tables that we may wish to refer to.
AN APPRAISAL OF THE CALCULATOR
The Bell Telephone Laboratories general-purpose relay computer is
probably the best mechanical brain made up to the end of 1947, in
regard to the two important factors of reliability and versatility.
Reliability
The machine produces results that are practically 100 per cent
reliable, for the machine checks each step before taking the next
one. The checking principle is that exactly a certain number of
relays must be energized. For example, as we said before, for each
decimal digit there are 7 relays. Exactly 2 of these relays must be
energized—no more, no less. If this does not happen, the machine stops
at once without losing any numbers. Lights shine for many circuits
in the control panel, and, if you compare what they ought to show
with what they do show, you can usually find at once the location of
the mistake. The trouble may be a speck of dirt between two contact
points on a relay, and, when it is brushed away, the machine can go
right ahead from where it stopped. According to a statement by Franz
L. Alt, director of the computing laboratory at the Ballistic Research
Laboratories, in December 1947, “the Bell machine had not given a
single wrong result in eight months of operation, except when operators
interfered with its normal running.”
To guard against the risk of putting tapes in the wrong transmitters,
the machine will check by the instructions contained in the tapes that
the right tapes are in the right places.
Time Required
The time required to do problems on this mechanical brain is perhaps
longer than on the others. The numbers are handled digit by digit on
the input tapes, and the typewriter in the recorder moves space by
space in order to get to the proper writing point. These are slow
procedures. The speeds of numerical operation are: addition, ³/₁₀
second; multiplication, 1 second on the average; division, 2.7 seconds
on the average; square root, 4.5 seconds on the average; logarithm,
about 15 seconds.
Staff
In order to operate the machine, the staff required is: one maintenance
man; one mathematical engineer; about six girls for punching tape,
etc., depending on the number of problems to be handled at the rate of
about one problem per week per girl. Unlike any of the other mechanical
brains built by the end of 1947, this machine will run unattended.
Maintenance
The relays in the machine will operate for years with no failure; they
have the experience of standard telephone techniques built into them.
Under laboratory conditions this type of relay had by 1946 operated
successfully much more than 100 million times. The tape feeding and
reading equipment in the machine may be maintained by periodic
inspection and service. The total number of teletype transmitters in
the machine is 38. If one fails, it is easy to plug in a spare.
The total power required for the machine is about 28 horsepower.
Batteries are furnished so that, if the power supply should be
interrupted, the machine can still operate for as long as a half-hour.
Cost
The cost of production of this machine in the size of 4 problem
positions and 2 computers has been roughly estimated as half a million
dollars. This cost includes material, manufacture, installation, and
testing. No development cost is included in this figure. Instead, the
cost of development has been reckoned as squaring with patents and
other contributions of the work to the telephone switching art.
It is unlikely that the general-purpose relay computer will be
manufactured generally. The pressure of orders for telephones, the
need to catch up with the backlog of demand, and the development of
electronic computers—all indicate that the Bell system will hardly
go further with this type of computer. In an emergency, however, the
Bell system would probably construct such machines for the government,
if requested. In the meantime, many principles first used in the
general-purpose relay computer are likely to find applications in
telephone system work. In fact, a present major development being
pursued in the telephone sections of Bell Laboratories is the
application of the computer principles to the automatic computation of
telephone bills.