24 Feb
2009
24 Feb
'09
10:34 p.m.
Paul Koning wrote:
So that's a ratio of about 67/1 of bit-size vs. oxide-to-head-distance (I'm
assuming 'dpi' is for bit-parallel 'digits' and hence equates to bpi).
It won't take too many increases in density before the two start coming into
'problem range'.
For the sake of comparison, one could take the average physical bit density or
head-gap-width of, for example, floppies of some type, and calculate the
equivalent ratio.
The thickness of the lamination moves the
magnetic medium away from
the
head,
reducing signal strength or S/N and maximum possible bit density.
I don't know what the density is on DECtapes but I presume it was
fairly low
and they could get away with the lamination, or they traded off bit
density for robustness.
Bitsavers has assorted DECtape documents, including a spec of the media.
It says the coating is 0.04 mil thick, so the magnetic media don't move
away much.
Density is quoted as 375 dpi, give or take, in a 1964 article also on
Bitsavers.