June 1955 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
The TRAnsistor DIgital Computer
- or TRansistorized Airborne DIgital Computer for the airborne version - built in
1954, was the first transistorized computer. It might more aptly be called the first
diode-ized digital computer since although it contained about 800 germanium transistors,
there were more than 11,000 diodes used in the diode-transistor logic (DTL), diode logic (DL),
and diode-resistor-logic (DRL) circuits. The TRADIC's construction benefitted in
numerous ways over the vacuum tube computers it replaced, most notably in increased
speed, smaller size, faster operations, higher reliability, greater safety (no high
voltages), and lower power consumption. Even with the relatively high price of transistors
compared to tubes in 1954, a mere six years after the transistor's invention, the
significantly lower cost of power supplies, simpler enclosure heat dissipation design,
fewer biasing and interstage components with their accompanying more complex assembly
would more than offset the transistor and diode cost. On a side note, I have to
believe that in the day someone - a competitor or disgruntled employee - replaced
the "D" in TRADIC with a "G."
TRADIC - The "Super Computer"
A Miniature electronic "brain" that can
operate flawlessly in planes flying at supersonic speed has been developed for the
U. S. Air Force by Bell Telephone Laboratories.
The "brain" is a digital computer which eliminates vacuum tube failure and heat,
jet aircraft's greatest electronic problems, by the use of transistors instead of
vacuum tubes. It contains nearly 800 of these tiny, solid devices and is believed
to be the first all- transistor computer designed for aircraft. Transistors, developed
at Bell Laboratories, are completely cold, highly efficient amplifying devices which
use very little power.
Known as "TRADIC" (TRansistor-DIgital-Computer), the new computer requires less
than 100 watts to operate. This is one - twentieth of the power needed by comparable
vacuum -tube computers. Early computers used as many as 18,000 vacuum tubes and
frequently required thousands of watts to operate.
The new electronic "brain" contains, in addition to transistors, nearly 11,000
germanium diodes, These serve as the electronic equivalent of tiny one-way switches.
Solid, like transistors, they are capable of operating thousands of times faster
than their mechanical counterparts.
Answers to trigonometric problems are furnished by series of
dots on oscilloscope. Dots move so fast they seem to form lines.
Transistor is inserted into one of TRADIC's "memory" packages.
These units store information until entire problem is solved.
Less power is needed to operate TRADIC than is required to light
a 100-watt bulb.
When design work has been completed, the computer will probably occupy less than
three cubic feet of the critical space in modern military aircraft. TRADIC can do
sixty thousand additions or subtractions, or three thousand multiplications or divisions
a second. A typical problem fed into the machine requires it to go through about
250 different steps of computation. It can run through an entire problem of that
complexity and provide an answer in about 15 thousandths of a second - much less
time than it takes to say "TRADIC." The computer can handle, simultaneously, as
many as thirteen 16-digit numbers. Mathematical instructions are placed into TRADIC
by means of a "plug-in" unit resembling a small breadboard. Plug-in units are set
up beforehand with interconnecting wires to represent problems at hand. Numbers
to be processed are put into the machine by means of simple switches. The laboratory
model of TRADIC provides answers to trigonometric problems with a series of "dots"
on an oscilloscope. These dots of light move so rapidly that they actually appear
to draw geometric diagrams on the scope.
To handle the successive steps of complex computation, a machine, like a human,
must have a means of storing information until it is needed. When a man works on
an involved mathematical problem, he usually jots down on paper the answer to each
section as it is solved, then refers back to this frequently as he proceeds. TRADIC,
however, automatically transfers each sub-answer to built-in "memory" packages while
continuing to tackle the remaining sections.
There are two main types of computers, digital and analog. A digital computer,
like the mileage indicator of a car, is a "counting" machine which clocks off one
number after another. Each digit shifts when the number to the right of it passes
nine. Digital computers can actually perform only additions or subtractions but
they are able to multiply or divide by successive additions or subtractions.
An analog computer might be likened to an automobile speedometer which represents
speed in terms of the angle of a pointer on the dial. An analog computer gives results
in terms of voltages, resistances or rotations. It is designed for a specific task
and cannot be easily adapted for another problem.
TRADIC, fundamentally a digital computer, has the advantage of being able to
operate on analog data.
Posted July 30, 2019