Electronic Design

Thin-Film Memory Gives Fast Output

A magnetic thin-film cylinder that contains features of the thin-film dot, the ferrite core, and the magnetic rod is bidding for an important role in future computer memories. Under development by CBS Laboratories of Stamford, Conn., the device, called the Toristor, is composed of a plating of nickel-iron-cobalt composition on a substrate of glass or stainless steel.

Like the conventional toroidal ferrite core, the Toristor has wires passing through its center. Its output voltage range, 50 to 250 mV, includes the 40- to 120-mV range of cores. But its write-read cycle time, as short as 15 nsec, is substantially faster than the 3 to 5 µsec of cores.

The Toristor's cycle time compares favorably with the very rapid 200 to 500 nsec of thin-film dots. And the rapidity of switching its magnetic domains, 10 to 15 nsec, compares well with the 5 to 40 nsec of dots. But its 50- to 250-mV output voltage range is a lot huskier than the 2 to 20 mV common with dots.

Like the magnetic rod, the Toristor takes a circumferential winding to provide a transverse interrogation field. But the Toristor also takes axial wires through its center for sense and digit write. The 300-mA digit-read current is the same as that required for other computer memories.

The principal advantage of the new development lies in its true, nondestructive readout. Other nondestructive elements, like the multiaperture devices, require priming before each read operation. The Toristor requires only the interrogation pulse, which can be unipolar. To save time, information in the Toristor can be changed during the interrogation interval.

Output from the Toristor is bipolar; a "one" is in the opposite direction from a "zero." With cores, the output for a "one" is represented by magnetization in the same direction as a "zero"—but of significantly different amplitude.

The principal difference between the Toristor and other devices is that its magnetic domains are rotated through angles less than 90°—that is, through their hard directions. This makes for far less sensitivity to variations in temperature and in the composition of the magnetic material. (Electronic Design, August 2, 1961, p. 26)

Although refinements continued to be made on toroidal magnetic cores, a lot of development effort was invested in other types of random-access magnetic storage devices. A wide variety of innovative configurations resulted, few of which actually made it into practical applications.

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