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

II-2
in a month; this is about the number of revolutions the average
automobile engine makes in 1CX3,000 miles o It is immediately apparent
that whatever means is used to move the magnetic medium cyclically
Relative to the reading station must be of carefully executed, long-
life design, as for example pivoted motion or simple rotation in suit-
able bearings. In particular, rubbing contact between the magnetic
medium and the pickup device seem fairly ruled out by this consideration,
since the wear at the point of contact would be prohibitive unless
lubrication were possible, and unless also it were possible to combine
the functions of a superb bearing with those of the pickup device
this seems unlikely. Therefore loops of magnetic wire running agsdnst
conventional magnetic heads are ruled out, and with them any type of
relative motion except simple rotation of medium relative to pickup,
with the provision of clearcince between.
3) An access time of ten milliseconds maximum implies (at
most) a cyclic speed on the order of 6000 R.P.tL This is certainly
within the bounds of nonrval engineering practice; many electric motors
are rated (and normally run) at higher speeds. Since the I.A.S. computing'
machine is non-synchronous there is no particular reason that this
speed should be constant; in fact, an ordinary polyphase induction motor
running at 7200 R»P.M„ with ten or fifteen percent slip should be
perfectly satisfactory. This could then be direct-coupled and, if
desired, the entire rotating system could run on the same set of bearings.
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