Microcomputer Circuits and Processes

This movement is accomplished by a rotating magnetic field which
drags the bubble around the chevrons and makes it jump across at the
appropriate time.
This rotating field is obtained by controlled currents passing
through two coils~aligned at right angles to each other, surrounding the
bubble-slice. The bias field is obtained by two permanent magnets
which maintain the bubbles in existence; so this is non-volatile memory.
The structure of the device is sketched in figure 4.8.
permanent
magnet
permanent
magnet
Figure 4.8
Structure of a megabit bubble memory device, showing permanent magnets producing
the bias field, orthogonal coils producing the rotating field. ('Exploded view'.)
To understand how this system of moving bubbles can be used as a
computer memory, we must look at how the loops of rotating bubbles
are arranged. This is shown in figure 4.9.
data out
~
~( IOO~300 )~
~(
: )~
~(
: )~ ! oulpul
track
;npUI!
track
~( :
)~
~( IO~O )~
Figure 4.9
Architecture of a bubble memory,
showing bubble loops and ~
input and output tracks.
data in
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