lo22 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 



coincident-current method. Consider a current pulse /i applied through 

 the nickel wire in such a direction as to enhance the spiraling flux, and 

 a second current pulse h applied by means of an external solenoid (see 

 Fig. 4). Coincidentally, the proper amplitude current pulses will switch 

 the flux state of the wire; either alone will not be sufficient. To sense the 

 state of the stored information it is necessary either to reverse both cur- 

 rents, or to overdrive Ii in the reverse direction. In an array, the output, 

 in the form of a voltage pulse, would be sensed across the ends of the 

 nickel wire. The solenoid may be replaced by a single copper conductor 

 passing at right angles to the nickel wire. For obvious reasons the mem- 

 ory cell has been named the "twistor". The above method of operation 

 will be referred to as mode A. 



Mode B is the use of the magnetic wire as a direct replacement for the 

 conventional coincident-current toroid. Its use here differs only in that 

 the wire itself is used as a sensing winding (refer to Fig. 5). The pulses 

 /i and 1-2 are eciual in value and each alone is chosen to be insufficient to 

 switch the magnetization state of the wire. The coincidence of /i and Ii 

 will, however, result in the writing of a bit of information into the wire. 

 To read, /i and I-i are reversed in polarity and applied coincidently. The 

 output appears as a voltage pulse across the ends of the nickel wire. 



Fig. 4 — Coincident currents for the "write" operation in a twistor operated 

 mode A. Wire under torsion. 



•SIGNAL 



^i'^" ^ 77 ^°^ mode B the coincidence of 7i and Ii is required to exceed the knee 

 ot the <(>~NI characteristic. Wire under torsion. 



