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

II-4
would be manageablco However, here another factor enters, namely,
the clearance-spacing betvveen the "read-write" device and the
magnetic surface o Clearly the packing density of magnetic spots
on the medium is critically related to this separation, and in
most conceivable circumstances by a greater power of this
separation interval than unity. For a single magnetic path on a
wtoeel 5 1/2 fto in diameter fabricated, for example, from aluminum
it is to be expected that temperature variations on the order of
ten degrees centigrade would produce variations in the clearance
on the order of six thousandths of an inch; and although design
ingenuity could certainly compensate part of this, still the
implied variations in the geom.etry are disturbingly large compared
to clearances sufficiently close to conditions of contact customarily
used in achieving packing densities near 100 to the linear inch.
6) Therefore, to achieve the desired scanning rate of at
least ^OOQCDO" spots" per second at reasonable peripheral speeds calls
for a system of several — say, ten — read-write heads; and if these
are to be operated at a close but finite and stable separation — say
oOOl inch — from the magnetic medium, then a radius for the rotating
system on the order of a few inches — say, three or four — is implied.
The multiplicity of reading stations discourages rotation of the read-
write system and encourages rotation of the magnetic medium in some
simple rigid geometric form — say a drum spihning about its sods; and
-finally, since the "spots" are assumed subject to examination in wholly
arbitrary sequence, this complete ignorance of priority implies uniform