In a period between 1947 to 1950, a device called the EDVAC (Electronic Discrete Variable Automatic Computer) was constructed at the Moore School of Electrical Engineering – University of Pennsylvania.
It was to be a much more powerful machine than the ENIAC but smaller, being of serial and synchronous design. It contained some 5,900 vacuum tubes and 12,000 semi-conductor diodes.
Unlike today’s machines that have words (bytes) designed to contain bits (binary digits) in the amounts of multiples of 2 (the TS-1000 uses the Z-80 micro-processor which is an 8-bit device), the EDVAC had 44-bit words.
The memory storage devices were unique for their day. Ultrasonic signals were were produced from electrical signals through an ULTRASONIC DELAY LINE. The sound pulses were then introduced into a container of mercury fluid.
Since the fluid would transmit the sound waves at a much slower rate than the original electrical pulses traveled through the wire, a delay was involved that would allow the ultrasonic delay line to change the sound pulses back into electrical pulses and perpetuate the effect continuously. The delay time was set by adjusting the length of the fluid container. Piezoelectric crystals, much like those in telephone receiver assemblies for sound transmission and reception, were responsible for the conversion of electrical impulses to sound and vice-versa.
John von Neumann, a distinguished computer consultant, had been hired by the Moore School to utilize his special talents, one of which was total mental recall or what we may call a photgraphic memory.
Neumann developed the first stored program, designed to sort and merge data. He also discovered that with the EDVAC’s design, parallel accumulators, such as those used by ENIAC (20 in all), could be done away with. The speed and serial operation of the new machine had made them obsolete.
Today, many of you have asked what the advantages of serial over parallel interfacing are and the advantage is primarily speed. The disadvantage is that serial interfacing usually requires additional programming for data transfer and also parallel interfacing techniques have improved where speed has increased tremendously.
The internal memory storage medium of EDVAC was comprised of 128 thermostatically controlled acoustic delay lines, each storing 384 bits of data as sound waves in the mercury fluid medium with the information circulating constantly through the line. 1024 bits or 128 eight bit words of fast access storage was available per fluid container with an access time of 48 to 384 microseconds.
The EDVAC had diode logic circuits which permitted mathematical subtraction operations to be performed directly rather than through reciprocal addition, such as the method used in the SUBTRACTION program on our FEB/83 cassette.
Average time for addition was 864 microseconds and for multiplication was 2900 microseconds. I/O media included paper tape, tele-typewriters and punched cards.
The computer projects at the Moore School attracted less funding and attention as years went on, and the staff began breaking up with some of them going to Princeton University.
Finally, in 1950 the EDVAC was moved to the Aberdeen proving grounds and the Moore School disbanded the ENIAC/EDVAC programs and staff, primarily because of disinterest.
By this time, however, a program at Princeton was in full swing with many of the former Moore School staff members, including von Neumann and the IAS computer was born. The development stage was from 1946 to 1952 and was primarily under von Neumann’s direction.
The IAS was a marvel in miniaturization for its time. Measuring only 2 by 8 feet, exclusive of I/O equipment, it contained some 2300 vacuum tubes (mostly double triodes) and was constructed of three registers.
The first housed a parallel adder, the second a control unit and the third an electrostatic memory composed of 40 CRTs. The electrostatic memory had a capacity of 1,024 forty bit words and each cathode ray tube (CRT) had an array of 32 X 32 = 1024 charged spots on the phosphor surface.
This electrostatic storage tube device was much faster than the ultrasonic-mercury fluid canister delay line. Negative numbers were represented by compliments. Multiplication was done by successive addition (see the MULTIPLY program, AUG/82 cassette for formula) and division by successive subtraction.
The IAS computer stored its programming instructions (early machine language) in the CRT memory which included commands for basic arithmetic operations, shifting, input, output, unconditional transfer and conditional transfer (branching).
The computer revolution was now gaining momentum throughout western Europe and the U.S. and before the IAS was completed, companies such as Rand Corporation and IBM already had projects started that made the IAS obsolete.
The mercury delay line used on the EDVAC, although slower than some of the newer devices, was not made obsolete yet and versions of it appeared on later computers such as the UNIVAC — Ed.