First progress report on a multi-channel magnetic drum inner ...

VI-8
pulse a shorter sequence of negative pulses was recorded ivith the
first negative pulse superimposed on the first positive pulse.
Photograph 1-g pictures the results at the point where the shorter
sequence terminat3d, i.e. w^en the resultant sequence of pulses
changes polarity. The pulses in this picture are packed $0 to the
inch.
These pictures show that at a packing density of 50 pulses to the
inch there is a distinct flat between pulses produced by adjacent
dipoles of the same polarity and that when two dipoles of opposite
polarity are adjacent the voltage produced by them returns to zero
between pulses. It is clear that sequences of pulses of arbitrary
polarity can be safely resolved at 50 to the inch without any
interference due to adjacent pulses. This packing density reflects
a safety factor of two to one, for the dynamic tests (as well as the
static tests based on the "extrapolated width" of Sections 6.1 and 6.2)
show that actually 100 pulses could be recorded per inch.
The pictures of superimposed pulses also show that new information
can be recorded where old information is stored without erasing the
old. For they show that it is possible, by means of a tinging pulse, to
induce a dipole of any desired polarity in a region vjhere a dipole of
the same or opposite polarity is recorded. This is a great advantage,
for it eliminates the necessity of devising a method of erasing infor-
mation without destroying the adjacent information. The drum system