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

air operating against a small turbine to turn the rotor, and a vacuum pump
system as prime mover. With such an arrangement rota.tional rates of 36,000
X-4
R.P.M. should prove easily feasible, and for a drum of about 3" diameter
this would allow roughly the same pulse spacing (.01") as now used. How-
ever, the use of partial vacumn about this rotor introduces a new problem,
since the breakdown voltage between various electrical conductors is
seriously reduced — so that the vi/riting pulse voltage may again become
the limitation.
To sum up, all of the critical factors appear to approach natural
bounds of practicality in the vicinity of 10 pulses per second per channel,
and at rotational speeds between 30,000 and 40,000 R.P.M. The number of
digits around each magnetic tract seen: also bounded somewhere between 2000
and 5000. Also with pulses of rou^ly half microsecond duration, the
techniques of "gating" and "counting" are not far from upper limits of
safe performance.
Accordingly, the limits of the r^agnetic drum memory technique
may be represented by a single channel of capacitj?- 5000 digits, scan rate
10 digits per second, and mean access time about 10"^ second. The
number of electronic tubes per channel would probably lie between 3 and 6,
If more than one read-write head be used, the rotational speed or the
access time could be proportionately reduced.
A typical example of the ultimate design using these techniques
might well be a unit such as the following: a drum of seven inch diameter,
duraluminum 24-ST, running 24,000 R.P.M. on cascaded concentric bearings,
having four read-write heads per channel and 45 channels, in an evacuated
housing and driven by air jet. This might have a total capacity of 2,500
words of 40 binary digits each, with mean access time of 10"^ second.