Efficiency
In many respects, this machine is efficient and well-balanced. Its reading and writing speed is close to its calculating speed. We can punch or print a result on the average for every 10 additions or 1½ multiplications. The memory of 72 numbers in the machine is extremely useful; a smaller memory is a serious limitation on the achievements of a computing machine. The machine can do many kinds of arithmetic and logic. It is well educated and can compute automatically some rather complicated mathematical functions, like logarithm or sine. It has done difficult and important problems. It has computed and tabulated ([see Supplement 2]) Bessel functions, definite integrals, etc. It can solve differential equations ([see Chapter 5]) and many other problems in mathematics, physics, and engineering.
On the other hand, no calculator will ever again be built just like this one, useful though it is. Electronic computing is easily 100 times as fast as relay computing; nearly every future calculator will do its computing electronically. Many other improvements will be made. For example, in this calculator, there are 72 addition-subtraction mechanisms, yet only one of these can be used at a time. Also, the machine has only one combined multiply-divide unit. So we have to organize any computation with few multiplications, and with still fewer divisions, for they take longer still.
Until 1947, we had to organize any computation in this calculator into one single fixed sequence of operations. In other words, there was no way to move from one subroutine to another subroutine depending on some indication that turned up in our computation. Recently, the Harvard Computation Laboratory decided to remedy this condition and provided the Subsidiary Sequence Mechanism equivalent to 10 subroutines of 22 lines of coding each. These are on relays and plug wires and may be called for by the sequence-control tape or by each other. This provision has added greatly to the efficiency of the calculator.
Whatever else can be said about the Harvard IBM Automatic Sequence-Controlled Calculator, it must be said that this was the first general-purpose mechanical brain using numbers in digit form and able to do arithmetic and logic in hundreds of thousands of steps one after another. And great credit must go to Professor Howard H. Aiken of Harvard and the men of International Business Machines Corporation who made this great mechanical brain come into existence.
Chapter 7
SPEED—5000 ADDITIONS A SECOND:
MOORE SCHOOL’S ENIAC
ELECTRONIC NUMERICAL INTEGRATOR AND CALCULATOR
Another of the giant brains that has begun to work is named ENIAC. This name comes from the initial letters of the full name, Electronic Numerical Integrator and Calculator. Eniac was born in 1942 at the Moore School of Electrical Engineering, of the University of Pennsylvania, in Philadelphia. Eniac’s father was the Ordnance Department of the U. S. Army, which provided the funds to feed and rear the prodigy.
In the short space of four years, Eniac grew to maturity, and in February 1946 he began to earn his own living by electronic thinking. Eniac promptly set several world’s records. He was the first giant brain to use electronic tubes for calculating. He was the first one to reach the speed of 5000 additions a second. He was the first piece of electronic apparatus containing as many as 18,000 electronic tubes all functioning together successfully. As soon as Eniac started thinking, he promptly made relay calculators obsolete from the scientific point of view, for they have a top speed of perhaps 10 additions a second.
At the age of 5, he moved to Maryland at a cost of about $90,000, and his permanent home is now the Ballistic Research Laboratories at the U. S. Army’s Proving Ground at Aberdeen, Md.