The Univac Solid State Computer 90.


Circuitboard with four ferractors (white).

Backside. (5 x 6 inches.)
Ferractors.

While computers are now composed of many integrated circuits, containing millions of logical units, 
processing data with a speed of a few gigabits per second in a parallel-flow of 64 bits, 
the USSC's CPU-logic was composed out of 1700 circuit boards, each with only a few active components.
One type of circuitboard contained only 4 simple logical units, ferractors circuits. 
These circuit-boards handled the data with the speed of 700 KBits/second.

The ferractors were tiny transformers, performing one-bit operations, powered by 700 KC/S 36Vtt AC.
On the positive half of the cycle, the ferractor-core was magnetized or not 
depending on the direction of a small current through the bias-coil. 
This made the total magnetic field in the core to exceed the hysteresis-threshold or not.
In the subsequent negative half-cycle of the AC-power the ferractor showed a high or a low impedance,  
depending on whether it had been magnetized or not. 
Since the bias-current was much smaller then the output-current was on low impedance, 
these circuits could be used as amplifiers in binary logics.
By using the bias coil in opposite directions, they built ferractor-circuits with inverting or non-inverting amplification.

Since each ferractor was set in one cycle-half and was read in the next half of the cycle, 
a bit always was delayed (stored) by half a cycle. 
By placing 24 ferractors in series, odd and even places fed by opposite phases of the AC-power, 
a string was formed in which 12 bits circled around. Four such chains parallel made a register, in which 10 digits, 
the sign and a gap were circling around. 
The gap was necessary for the switching in read and write operations, also it enhanced the shortening of a register, 
what would make a number to shift one (decimal) position to the left each wordtime. 

A single ferractor. Note the detail of the coil: it was handmade !

Diodes

The 200 diode-boards were used in OR and in NAND functions, depending on being located within positive or negative logic. Simple diode-circuits performed all the logic within the CPU.

Transistors

Transistors were used to amplify tiny signals, like for the signals from the magnetic-heads, reading the magnetic-drum. And they were used for interfacing the ferractor-cicuits with the relais and the lamps. Note that the design of this computer started in (+-) 1955 and the germanium-transistor was only eight years old then.

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